core/fmt/mod.rs
1//! Utilities for formatting and printing strings.
2
3#![stable(feature = "rust1", since = "1.0.0")]
4
5use crate::cell::{Cell, Ref, RefCell, RefMut, SyncUnsafeCell, UnsafeCell};
6use crate::char::{EscapeDebugExtArgs, MAX_LEN_UTF8};
7use crate::marker::PhantomData;
8use crate::num::fmt as numfmt;
9use crate::ops::Deref;
10use crate::{iter, mem, result, str};
11
12mod builders;
13#[cfg(not(no_fp_fmt_parse))]
14mod float;
15#[cfg(no_fp_fmt_parse)]
16mod nofloat;
17mod num;
18mod rt;
19
20#[stable(feature = "fmt_flags_align", since = "1.28.0")]
21#[cfg_attr(not(test), rustc_diagnostic_item = "Alignment")]
22/// Possible alignments returned by `Formatter::align`
23#[derive(Copy, Clone, Debug, PartialEq, Eq)]
24pub enum Alignment {
25 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
26 /// Indication that contents should be left-aligned.
27 Left,
28 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
29 /// Indication that contents should be right-aligned.
30 Right,
31 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
32 /// Indication that contents should be center-aligned.
33 Center,
34}
35
36#[doc(hidden)]
37#[unstable(feature = "fmt_internals", reason = "internal to standard library", issue = "none")]
38impl From<rt::Alignment> for Option<Alignment> {
39 fn from(value: rt::Alignment) -> Self {
40 match value {
41 rt::Alignment::Left => Some(Alignment::Left),
42 rt::Alignment::Right => Some(Alignment::Right),
43 rt::Alignment::Center => Some(Alignment::Center),
44 rt::Alignment::Unknown => None,
45 }
46 }
47}
48
49#[stable(feature = "debug_builders", since = "1.2.0")]
50pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
51#[unstable(feature = "debug_closure_helpers", issue = "117729")]
52pub use self::builders::{FromFn, from_fn};
53
54/// The type returned by formatter methods.
55///
56/// # Examples
57///
58/// ```
59/// use std::fmt;
60///
61/// #[derive(Debug)]
62/// struct Triangle {
63/// a: f32,
64/// b: f32,
65/// c: f32
66/// }
67///
68/// impl fmt::Display for Triangle {
69/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
70/// write!(f, "({}, {}, {})", self.a, self.b, self.c)
71/// }
72/// }
73///
74/// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 };
75///
76/// assert_eq!(format!("{pythagorean_triple}"), "(3, 4, 5)");
77/// ```
78#[stable(feature = "rust1", since = "1.0.0")]
79pub type Result = result::Result<(), Error>;
80
81/// The error type which is returned from formatting a message into a stream.
82///
83/// This type does not support transmission of an error other than that an error
84/// occurred. This is because, despite the existence of this error,
85/// string formatting is considered an infallible operation.
86/// `fmt()` implementors should not return this `Error` unless they received it from their
87/// [`Formatter`]. The only time your code should create a new instance of this
88/// error is when implementing `fmt::Write`, in order to cancel the formatting operation when
89/// writing to the underlying stream fails.
90///
91/// Any extra information must be arranged to be transmitted through some other means,
92/// such as storing it in a field to be consulted after the formatting operation has been
93/// cancelled. (For example, this is how [`std::io::Write::write_fmt()`] propagates IO errors
94/// during writing.)
95///
96/// This type, `fmt::Error`, should not be
97/// confused with [`std::io::Error`] or [`std::error::Error`], which you may also
98/// have in scope.
99///
100/// [`std::io::Error`]: ../../std/io/struct.Error.html
101/// [`std::io::Write::write_fmt()`]: ../../std/io/trait.Write.html#method.write_fmt
102/// [`std::error::Error`]: ../../std/error/trait.Error.html
103///
104/// # Examples
105///
106/// ```rust
107/// use std::fmt::{self, write};
108///
109/// let mut output = String::new();
110/// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) {
111/// panic!("An error occurred");
112/// }
113/// ```
114#[stable(feature = "rust1", since = "1.0.0")]
115#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
116pub struct Error;
117
118/// A trait for writing or formatting into Unicode-accepting buffers or streams.
119///
120/// This trait only accepts UTF-8–encoded data and is not [flushable]. If you only
121/// want to accept Unicode and you don't need flushing, you should implement this trait;
122/// otherwise you should implement [`std::io::Write`].
123///
124/// [`std::io::Write`]: ../../std/io/trait.Write.html
125/// [flushable]: ../../std/io/trait.Write.html#tymethod.flush
126#[stable(feature = "rust1", since = "1.0.0")]
127pub trait Write {
128 /// Writes a string slice into this writer, returning whether the write
129 /// succeeded.
130 ///
131 /// This method can only succeed if the entire string slice was successfully
132 /// written, and this method will not return until all data has been
133 /// written or an error occurs.
134 ///
135 /// # Errors
136 ///
137 /// This function will return an instance of [`std::fmt::Error`][Error] on error.
138 ///
139 /// The purpose of that error is to abort the formatting operation when the underlying
140 /// destination encounters some error preventing it from accepting more text;
141 /// in particular, it does not communicate any information about *what* error occurred.
142 /// It should generally be propagated rather than handled, at least when implementing
143 /// formatting traits.
144 ///
145 /// # Examples
146 ///
147 /// ```
148 /// use std::fmt::{Error, Write};
149 ///
150 /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
151 /// f.write_str(s)
152 /// }
153 ///
154 /// let mut buf = String::new();
155 /// writer(&mut buf, "hola")?;
156 /// assert_eq!(&buf, "hola");
157 /// # std::fmt::Result::Ok(())
158 /// ```
159 #[stable(feature = "rust1", since = "1.0.0")]
160 fn write_str(&mut self, s: &str) -> Result;
161
162 /// Writes a [`char`] into this writer, returning whether the write succeeded.
163 ///
164 /// A single [`char`] may be encoded as more than one byte.
165 /// This method can only succeed if the entire byte sequence was successfully
166 /// written, and this method will not return until all data has been
167 /// written or an error occurs.
168 ///
169 /// # Errors
170 ///
171 /// This function will return an instance of [`Error`] on error.
172 ///
173 /// # Examples
174 ///
175 /// ```
176 /// use std::fmt::{Error, Write};
177 ///
178 /// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
179 /// f.write_char(c)
180 /// }
181 ///
182 /// let mut buf = String::new();
183 /// writer(&mut buf, 'a')?;
184 /// writer(&mut buf, 'b')?;
185 /// assert_eq!(&buf, "ab");
186 /// # std::fmt::Result::Ok(())
187 /// ```
188 #[stable(feature = "fmt_write_char", since = "1.1.0")]
189 fn write_char(&mut self, c: char) -> Result {
190 self.write_str(c.encode_utf8(&mut [0; MAX_LEN_UTF8]))
191 }
192
193 /// Glue for usage of the [`write!`] macro with implementors of this trait.
194 ///
195 /// This method should generally not be invoked manually, but rather through
196 /// the [`write!`] macro itself.
197 ///
198 /// # Errors
199 ///
200 /// This function will return an instance of [`Error`] on error. Please see
201 /// [write_str](Write::write_str) for details.
202 ///
203 /// # Examples
204 ///
205 /// ```
206 /// use std::fmt::{Error, Write};
207 ///
208 /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
209 /// f.write_fmt(format_args!("{s}"))
210 /// }
211 ///
212 /// let mut buf = String::new();
213 /// writer(&mut buf, "world")?;
214 /// assert_eq!(&buf, "world");
215 /// # std::fmt::Result::Ok(())
216 /// ```
217 #[stable(feature = "rust1", since = "1.0.0")]
218 fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
219 // We use a specialization for `Sized` types to avoid an indirection
220 // through `&mut self`
221 trait SpecWriteFmt {
222 fn spec_write_fmt(self, args: Arguments<'_>) -> Result;
223 }
224
225 impl<W: Write + ?Sized> SpecWriteFmt for &mut W {
226 #[inline]
227 default fn spec_write_fmt(mut self, args: Arguments<'_>) -> Result {
228 if let Some(s) = args.as_statically_known_str() {
229 self.write_str(s)
230 } else {
231 write(&mut self, args)
232 }
233 }
234 }
235
236 impl<W: Write> SpecWriteFmt for &mut W {
237 #[inline]
238 fn spec_write_fmt(self, args: Arguments<'_>) -> Result {
239 if let Some(s) = args.as_statically_known_str() {
240 self.write_str(s)
241 } else {
242 write(self, args)
243 }
244 }
245 }
246
247 self.spec_write_fmt(args)
248 }
249}
250
251#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
252impl<W: Write + ?Sized> Write for &mut W {
253 fn write_str(&mut self, s: &str) -> Result {
254 (**self).write_str(s)
255 }
256
257 fn write_char(&mut self, c: char) -> Result {
258 (**self).write_char(c)
259 }
260
261 fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
262 (**self).write_fmt(args)
263 }
264}
265
266/// The signedness of a [`Formatter`] (or of a [`FormattingOptions`]).
267#[derive(Copy, Clone, Debug, PartialEq, Eq)]
268#[unstable(feature = "formatting_options", issue = "118117")]
269pub enum Sign {
270 /// Represents the `+` flag.
271 Plus,
272 /// Represents the `-` flag.
273 Minus,
274}
275
276/// Specifies whether the [`Debug`] trait should use lower-/upper-case
277/// hexadecimal or normal integers.
278#[derive(Copy, Clone, Debug, PartialEq, Eq)]
279#[unstable(feature = "formatting_options", issue = "118117")]
280pub enum DebugAsHex {
281 /// Use lower-case hexadecimal integers for the `Debug` trait (like [the `x?` type](../../std/fmt/index.html#formatting-traits)).
282 Lower,
283 /// Use upper-case hexadecimal integers for the `Debug` trait (like [the `X?` type](../../std/fmt/index.html#formatting-traits)).
284 Upper,
285}
286
287/// Options for formatting.
288///
289/// `FormattingOptions` is a [`Formatter`] without an attached [`Write`] trait.
290/// It is mainly used to construct `Formatter` instances.
291#[derive(Copy, Clone, Debug, PartialEq, Eq)]
292#[unstable(feature = "formatting_options", issue = "118117")]
293pub struct FormattingOptions {
294 flags: u32,
295 fill: char,
296 align: Option<Alignment>,
297 width: Option<u16>,
298 precision: Option<u16>,
299}
300
301impl FormattingOptions {
302 /// Construct a new `FormatterBuilder` with the supplied `Write` trait
303 /// object for output that is equivalent to the `{}` formatting
304 /// specifier:
305 ///
306 /// - no flags,
307 /// - filled with spaces,
308 /// - no alignment,
309 /// - no width,
310 /// - no precision, and
311 /// - no [`DebugAsHex`] output mode.
312 #[unstable(feature = "formatting_options", issue = "118117")]
313 pub const fn new() -> Self {
314 Self { flags: 0, fill: ' ', align: None, width: None, precision: None }
315 }
316
317 /// Sets or removes the sign (the `+` or the `-` flag).
318 ///
319 /// - `+`: This is intended for numeric types and indicates that the sign
320 /// should always be printed. By default only the negative sign of signed
321 /// values is printed, and the sign of positive or unsigned values is
322 /// omitted. This flag indicates that the correct sign (+ or -) should
323 /// always be printed.
324 /// - `-`: Currently not used
325 #[unstable(feature = "formatting_options", issue = "118117")]
326 pub fn sign(&mut self, sign: Option<Sign>) -> &mut Self {
327 self.flags =
328 self.flags & !(1 << rt::Flag::SignMinus as u32 | 1 << rt::Flag::SignPlus as u32);
329 match sign {
330 None => {}
331 Some(Sign::Plus) => self.flags |= 1 << rt::Flag::SignPlus as u32,
332 Some(Sign::Minus) => self.flags |= 1 << rt::Flag::SignMinus as u32,
333 }
334 self
335 }
336 /// Sets or unsets the `0` flag.
337 ///
338 /// This is used to indicate for integer formats that the padding to width should both be done with a 0 character as well as be sign-aware
339 #[unstable(feature = "formatting_options", issue = "118117")]
340 pub fn sign_aware_zero_pad(&mut self, sign_aware_zero_pad: bool) -> &mut Self {
341 if sign_aware_zero_pad {
342 self.flags |= 1 << rt::Flag::SignAwareZeroPad as u32
343 } else {
344 self.flags &= !(1 << rt::Flag::SignAwareZeroPad as u32)
345 }
346 self
347 }
348 /// Sets or unsets the `#` flag.
349 ///
350 /// This flag indicates that the "alternate" form of printing should be
351 /// used. The alternate forms are:
352 /// - [`Debug`] : pretty-print the [`Debug`] formatting (adds linebreaks and indentation)
353 /// - [`LowerHex`] as well as [`UpperHex`] - precedes the argument with a `0x`
354 /// - [`Octal`] - precedes the argument with a `0b`
355 /// - [`Binary`] - precedes the argument with a `0o`
356 #[unstable(feature = "formatting_options", issue = "118117")]
357 pub fn alternate(&mut self, alternate: bool) -> &mut Self {
358 if alternate {
359 self.flags |= 1 << rt::Flag::Alternate as u32
360 } else {
361 self.flags &= !(1 << rt::Flag::Alternate as u32)
362 }
363 self
364 }
365 /// Sets the fill character.
366 ///
367 /// The optional fill character and alignment is provided normally in
368 /// conjunction with the width parameter. This indicates that if the value
369 /// being formatted is smaller than width some extra characters will be
370 /// printed around it.
371 #[unstable(feature = "formatting_options", issue = "118117")]
372 pub fn fill(&mut self, fill: char) -> &mut Self {
373 self.fill = fill;
374 self
375 }
376 /// Sets or removes the alignment.
377 ///
378 /// The alignment specifies how the value being formatted should be
379 /// positioned if it is smaller than the width of the formatter.
380 #[unstable(feature = "formatting_options", issue = "118117")]
381 pub fn align(&mut self, align: Option<Alignment>) -> &mut Self {
382 self.align = align;
383 self
384 }
385 /// Sets or removes the width.
386 ///
387 /// This is a parameter for the “minimum width” that the format should take
388 /// up. If the value’s string does not fill up this many characters, then
389 /// the padding specified by [`FormattingOptions::fill`]/[`FormattingOptions::align`]
390 /// will be used to take up the required space.
391 #[unstable(feature = "formatting_options", issue = "118117")]
392 pub fn width(&mut self, width: Option<u16>) -> &mut Self {
393 self.width = width;
394 self
395 }
396 /// Sets or removes the precision.
397 ///
398 /// - For non-numeric types, this can be considered a “maximum width”. If
399 /// the resulting string is longer than this width, then it is truncated
400 /// down to this many characters and that truncated value is emitted with
401 /// proper fill, alignment and width if those parameters are set.
402 /// - For integral types, this is ignored.
403 /// - For floating-point types, this indicates how many digits after the
404 /// decimal point should be printed.
405 #[unstable(feature = "formatting_options", issue = "118117")]
406 pub fn precision(&mut self, precision: Option<u16>) -> &mut Self {
407 self.precision = precision;
408 self
409 }
410 /// Specifies whether the [`Debug`] trait should use lower-/upper-case
411 /// hexadecimal or normal integers
412 #[unstable(feature = "formatting_options", issue = "118117")]
413 pub fn debug_as_hex(&mut self, debug_as_hex: Option<DebugAsHex>) -> &mut Self {
414 self.flags = self.flags
415 & !(1 << rt::Flag::DebugUpperHex as u32 | 1 << rt::Flag::DebugLowerHex as u32);
416 match debug_as_hex {
417 None => {}
418 Some(DebugAsHex::Upper) => self.flags |= 1 << rt::Flag::DebugUpperHex as u32,
419 Some(DebugAsHex::Lower) => self.flags |= 1 << rt::Flag::DebugLowerHex as u32,
420 }
421 self
422 }
423
424 /// Returns the current sign (the `+` or the `-` flag).
425 #[unstable(feature = "formatting_options", issue = "118117")]
426 pub const fn get_sign(&self) -> Option<Sign> {
427 const SIGN_PLUS_BITFIELD: u32 = 1 << rt::Flag::SignPlus as u32;
428 const SIGN_MINUS_BITFIELD: u32 = 1 << rt::Flag::SignMinus as u32;
429 match self.flags & ((1 << rt::Flag::SignPlus as u32) | (1 << rt::Flag::SignMinus as u32)) {
430 SIGN_PLUS_BITFIELD => Some(Sign::Plus),
431 SIGN_MINUS_BITFIELD => Some(Sign::Minus),
432 0 => None,
433 _ => panic!("Invalid sign bits set in flags"),
434 }
435 }
436 /// Returns the current `0` flag.
437 #[unstable(feature = "formatting_options", issue = "118117")]
438 pub const fn get_sign_aware_zero_pad(&self) -> bool {
439 self.flags & (1 << rt::Flag::SignAwareZeroPad as u32) != 0
440 }
441 /// Returns the current `#` flag.
442 #[unstable(feature = "formatting_options", issue = "118117")]
443 pub const fn get_alternate(&self) -> bool {
444 self.flags & (1 << rt::Flag::Alternate as u32) != 0
445 }
446 /// Returns the current fill character.
447 #[unstable(feature = "formatting_options", issue = "118117")]
448 pub const fn get_fill(&self) -> char {
449 self.fill
450 }
451 /// Returns the current alignment.
452 #[unstable(feature = "formatting_options", issue = "118117")]
453 pub const fn get_align(&self) -> Option<Alignment> {
454 self.align
455 }
456 /// Returns the current width.
457 #[unstable(feature = "formatting_options", issue = "118117")]
458 pub const fn get_width(&self) -> Option<u16> {
459 self.width
460 }
461 /// Returns the current precision.
462 #[unstable(feature = "formatting_options", issue = "118117")]
463 pub const fn get_precision(&self) -> Option<u16> {
464 self.precision
465 }
466 /// Returns the current precision.
467 #[unstable(feature = "formatting_options", issue = "118117")]
468 pub const fn get_debug_as_hex(&self) -> Option<DebugAsHex> {
469 const DEBUG_UPPER_BITFIELD: u32 = 1 << rt::Flag::DebugUpperHex as u32;
470 const DEBUG_LOWER_BITFIELD: u32 = 1 << rt::Flag::DebugLowerHex as u32;
471 match self.flags
472 & ((1 << rt::Flag::DebugUpperHex as u32) | (1 << rt::Flag::DebugLowerHex as u32))
473 {
474 DEBUG_UPPER_BITFIELD => Some(DebugAsHex::Upper),
475 DEBUG_LOWER_BITFIELD => Some(DebugAsHex::Lower),
476 0 => None,
477 _ => panic!("Invalid hex debug bits set in flags"),
478 }
479 }
480
481 /// Creates a [`Formatter`] that writes its output to the given [`Write`] trait.
482 ///
483 /// You may alternatively use [`Formatter::new()`].
484 #[unstable(feature = "formatting_options", issue = "118117")]
485 pub fn create_formatter<'a>(self, write: &'a mut (dyn Write + 'a)) -> Formatter<'a> {
486 Formatter { options: self, buf: write }
487 }
488
489 #[doc(hidden)]
490 #[unstable(
491 feature = "fmt_internals",
492 reason = "internal routines only exposed for testing",
493 issue = "none"
494 )]
495 /// Flags for formatting
496 pub fn flags(&mut self, flags: u32) {
497 self.flags = flags
498 }
499 #[doc(hidden)]
500 #[unstable(
501 feature = "fmt_internals",
502 reason = "internal routines only exposed for testing",
503 issue = "none"
504 )]
505 /// Flags for formatting
506 pub fn get_flags(&self) -> u32 {
507 self.flags
508 }
509}
510
511#[unstable(feature = "formatting_options", issue = "118117")]
512impl Default for FormattingOptions {
513 /// Same as [`FormattingOptions::new()`].
514 fn default() -> Self {
515 // The `#[derive(Default)]` implementation would set `fill` to `\0` instead of space.
516 Self::new()
517 }
518}
519
520/// Configuration for formatting.
521///
522/// A `Formatter` represents various options related to formatting. Users do not
523/// construct `Formatter`s directly; a mutable reference to one is passed to
524/// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`].
525///
526/// To interact with a `Formatter`, you'll call various methods to change the
527/// various options related to formatting. For examples, please see the
528/// documentation of the methods defined on `Formatter` below.
529#[allow(missing_debug_implementations)]
530#[stable(feature = "rust1", since = "1.0.0")]
531#[rustc_diagnostic_item = "Formatter"]
532pub struct Formatter<'a> {
533 options: FormattingOptions,
534
535 buf: &'a mut (dyn Write + 'a),
536}
537
538impl<'a> Formatter<'a> {
539 /// Creates a new formatter with given [`FormattingOptions`].
540 ///
541 /// If `write` is a reference to a formatter, it is recommended to use
542 /// [`Formatter::with_options`] instead as this can borrow the underlying
543 /// `write`, thereby bypassing one layer of indirection.
544 ///
545 /// You may alternatively use [`FormattingOptions::create_formatter()`].
546 #[unstable(feature = "formatting_options", issue = "118117")]
547 pub fn new(write: &'a mut (dyn Write + 'a), options: FormattingOptions) -> Self {
548 Formatter { options, buf: write }
549 }
550
551 /// Creates a new formatter based on this one with given [`FormattingOptions`].
552 #[unstable(feature = "formatting_options", issue = "118117")]
553 pub fn with_options<'b>(&'b mut self, options: FormattingOptions) -> Formatter<'b> {
554 Formatter { options, buf: self.buf }
555 }
556}
557
558/// This structure represents a safely precompiled version of a format string
559/// and its arguments. This cannot be generated at runtime because it cannot
560/// safely be done, so no constructors are given and the fields are private
561/// to prevent modification.
562///
563/// The [`format_args!`] macro will safely create an instance of this structure.
564/// The macro validates the format string at compile-time so usage of the
565/// [`write()`] and [`format()`] functions can be safely performed.
566///
567/// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug`
568/// and `Display` contexts as seen below. The example also shows that `Debug`
569/// and `Display` format to the same thing: the interpolated format string
570/// in `format_args!`.
571///
572/// ```rust
573/// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
574/// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
575/// assert_eq!("1 foo 2", display);
576/// assert_eq!(display, debug);
577/// ```
578///
579/// [`format()`]: ../../std/fmt/fn.format.html
580#[lang = "format_arguments"]
581#[stable(feature = "rust1", since = "1.0.0")]
582#[derive(Copy, Clone)]
583pub struct Arguments<'a> {
584 // Format string pieces to print.
585 pieces: &'a [&'static str],
586
587 // Placeholder specs, or `None` if all specs are default (as in "{}{}").
588 fmt: Option<&'a [rt::Placeholder]>,
589
590 // Dynamic arguments for interpolation, to be interleaved with string
591 // pieces. (Every argument is preceded by a string piece.)
592 args: &'a [rt::Argument<'a>],
593}
594
595/// Used by the format_args!() macro to create a fmt::Arguments object.
596#[doc(hidden)]
597#[unstable(feature = "fmt_internals", issue = "none")]
598impl<'a> Arguments<'a> {
599 #[inline]
600 pub const fn new_const<const N: usize>(pieces: &'a [&'static str; N]) -> Self {
601 const { assert!(N <= 1) };
602 Arguments { pieces, fmt: None, args: &[] }
603 }
604
605 /// When using the format_args!() macro, this function is used to generate the
606 /// Arguments structure.
607 #[inline]
608 pub const fn new_v1<const P: usize, const A: usize>(
609 pieces: &'a [&'static str; P],
610 args: &'a [rt::Argument<'a>; A],
611 ) -> Arguments<'a> {
612 const { assert!(P >= A && P <= A + 1, "invalid args") }
613 Arguments { pieces, fmt: None, args }
614 }
615
616 /// Specifies nonstandard formatting parameters.
617 ///
618 /// An `rt::UnsafeArg` is required because the following invariants must be held
619 /// in order for this function to be safe:
620 /// 1. The `pieces` slice must be at least as long as `fmt`.
621 /// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
622 /// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.
623 #[inline]
624 pub const fn new_v1_formatted(
625 pieces: &'a [&'static str],
626 args: &'a [rt::Argument<'a>],
627 fmt: &'a [rt::Placeholder],
628 _unsafe_arg: rt::UnsafeArg,
629 ) -> Arguments<'a> {
630 Arguments { pieces, fmt: Some(fmt), args }
631 }
632
633 /// Estimates the length of the formatted text.
634 ///
635 /// This is intended to be used for setting initial `String` capacity
636 /// when using `format!`. Note: this is neither the lower nor upper bound.
637 #[inline]
638 pub fn estimated_capacity(&self) -> usize {
639 let pieces_length: usize = self.pieces.iter().map(|x| x.len()).sum();
640
641 if self.args.is_empty() {
642 pieces_length
643 } else if !self.pieces.is_empty() && self.pieces[0].is_empty() && pieces_length < 16 {
644 // If the format string starts with an argument,
645 // don't preallocate anything, unless length
646 // of pieces is significant.
647 0
648 } else {
649 // There are some arguments, so any additional push
650 // will reallocate the string. To avoid that,
651 // we're "pre-doubling" the capacity here.
652 pieces_length.checked_mul(2).unwrap_or(0)
653 }
654 }
655}
656
657impl<'a> Arguments<'a> {
658 /// Gets the formatted string, if it has no arguments to be formatted at runtime.
659 ///
660 /// This can be used to avoid allocations in some cases.
661 ///
662 /// # Guarantees
663 ///
664 /// For `format_args!("just a literal")`, this function is guaranteed to
665 /// return `Some("just a literal")`.
666 ///
667 /// For most cases with placeholders, this function will return `None`.
668 ///
669 /// However, the compiler may perform optimizations that can cause this
670 /// function to return `Some(_)` even if the format string contains
671 /// placeholders. For example, `format_args!("Hello, {}!", "world")` may be
672 /// optimized to `format_args!("Hello, world!")`, such that `as_str()`
673 /// returns `Some("Hello, world!")`.
674 ///
675 /// The behavior for anything but the trivial case (without placeholders)
676 /// is not guaranteed, and should not be relied upon for anything other
677 /// than optimization.
678 ///
679 /// # Examples
680 ///
681 /// ```rust
682 /// use std::fmt::Arguments;
683 ///
684 /// fn write_str(_: &str) { /* ... */ }
685 ///
686 /// fn write_fmt(args: &Arguments<'_>) {
687 /// if let Some(s) = args.as_str() {
688 /// write_str(s)
689 /// } else {
690 /// write_str(&args.to_string());
691 /// }
692 /// }
693 /// ```
694 ///
695 /// ```rust
696 /// assert_eq!(format_args!("hello").as_str(), Some("hello"));
697 /// assert_eq!(format_args!("").as_str(), Some(""));
698 /// assert_eq!(format_args!("{:?}", std::env::current_dir()).as_str(), None);
699 /// ```
700 #[stable(feature = "fmt_as_str", since = "1.52.0")]
701 #[rustc_const_stable(feature = "const_arguments_as_str", since = "1.84.0")]
702 #[must_use]
703 #[inline]
704 pub const fn as_str(&self) -> Option<&'static str> {
705 match (self.pieces, self.args) {
706 ([], []) => Some(""),
707 ([s], []) => Some(s),
708 _ => None,
709 }
710 }
711
712 /// Same as [`Arguments::as_str`], but will only return `Some(s)` if it can be determined at compile time.
713 #[must_use]
714 #[inline]
715 fn as_statically_known_str(&self) -> Option<&'static str> {
716 let s = self.as_str();
717 if core::intrinsics::is_val_statically_known(s.is_some()) { s } else { None }
718 }
719}
720
721// Manually implementing these results in better error messages.
722#[stable(feature = "rust1", since = "1.0.0")]
723impl !Send for Arguments<'_> {}
724#[stable(feature = "rust1", since = "1.0.0")]
725impl !Sync for Arguments<'_> {}
726
727#[stable(feature = "rust1", since = "1.0.0")]
728impl Debug for Arguments<'_> {
729 fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
730 Display::fmt(self, fmt)
731 }
732}
733
734#[stable(feature = "rust1", since = "1.0.0")]
735impl Display for Arguments<'_> {
736 fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
737 write(fmt.buf, *self)
738 }
739}
740
741/// `?` formatting.
742///
743/// `Debug` should format the output in a programmer-facing, debugging context.
744///
745/// Generally speaking, you should just `derive` a `Debug` implementation.
746///
747/// When used with the alternate format specifier `#?`, the output is pretty-printed.
748///
749/// For more information on formatters, see [the module-level documentation][module].
750///
751/// [module]: ../../std/fmt/index.html
752///
753/// This trait can be used with `#[derive]` if all fields implement `Debug`. When
754/// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
755/// comma-separated list of each field's name and `Debug` value, then `}`. For
756/// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
757/// `Debug` values of the fields, then `)`.
758///
759/// # Stability
760///
761/// Derived `Debug` formats are not stable, and so may change with future Rust
762/// versions. Additionally, `Debug` implementations of types provided by the
763/// standard library (`std`, `core`, `alloc`, etc.) are not stable, and
764/// may also change with future Rust versions.
765///
766/// # Examples
767///
768/// Deriving an implementation:
769///
770/// ```
771/// #[derive(Debug)]
772/// struct Point {
773/// x: i32,
774/// y: i32,
775/// }
776///
777/// let origin = Point { x: 0, y: 0 };
778///
779/// assert_eq!(
780/// format!("The origin is: {origin:?}"),
781/// "The origin is: Point { x: 0, y: 0 }",
782/// );
783/// ```
784///
785/// Manually implementing:
786///
787/// ```
788/// use std::fmt;
789///
790/// struct Point {
791/// x: i32,
792/// y: i32,
793/// }
794///
795/// impl fmt::Debug for Point {
796/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
797/// f.debug_struct("Point")
798/// .field("x", &self.x)
799/// .field("y", &self.y)
800/// .finish()
801/// }
802/// }
803///
804/// let origin = Point { x: 0, y: 0 };
805///
806/// assert_eq!(
807/// format!("The origin is: {origin:?}"),
808/// "The origin is: Point { x: 0, y: 0 }",
809/// );
810/// ```
811///
812/// There are a number of helper methods on the [`Formatter`] struct to help you with manual
813/// implementations, such as [`debug_struct`].
814///
815/// [`debug_struct`]: Formatter::debug_struct
816///
817/// Types that do not wish to use the standard suite of debug representations
818/// provided by the `Formatter` trait (`debug_struct`, `debug_tuple`,
819/// `debug_list`, `debug_set`, `debug_map`) can do something totally custom by
820/// manually writing an arbitrary representation to the `Formatter`.
821///
822/// ```
823/// # use std::fmt;
824/// # struct Point {
825/// # x: i32,
826/// # y: i32,
827/// # }
828/// #
829/// impl fmt::Debug for Point {
830/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
831/// write!(f, "Point [{} {}]", self.x, self.y)
832/// }
833/// }
834/// ```
835///
836/// `Debug` implementations using either `derive` or the debug builder API
837/// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`.
838///
839/// Pretty-printing with `#?`:
840///
841/// ```
842/// #[derive(Debug)]
843/// struct Point {
844/// x: i32,
845/// y: i32,
846/// }
847///
848/// let origin = Point { x: 0, y: 0 };
849///
850/// let expected = "The origin is: Point {
851/// x: 0,
852/// y: 0,
853/// }";
854/// assert_eq!(format!("The origin is: {origin:#?}"), expected);
855/// ```
856
857#[stable(feature = "rust1", since = "1.0.0")]
858#[rustc_on_unimplemented(
859 on(
860 crate_local,
861 label = "`{Self}` cannot be formatted using `{{:?}}`",
862 note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {Debug} for {Self}`"
863 ),
864 message = "`{Self}` doesn't implement `{Debug}`",
865 label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`"
866)]
867#[doc(alias = "{:?}")]
868#[rustc_diagnostic_item = "Debug"]
869#[rustc_trivial_field_reads]
870pub trait Debug {
871 #[doc = include_str!("fmt_trait_method_doc.md")]
872 ///
873 /// # Examples
874 ///
875 /// ```
876 /// use std::fmt;
877 ///
878 /// struct Position {
879 /// longitude: f32,
880 /// latitude: f32,
881 /// }
882 ///
883 /// impl fmt::Debug for Position {
884 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
885 /// f.debug_tuple("")
886 /// .field(&self.longitude)
887 /// .field(&self.latitude)
888 /// .finish()
889 /// }
890 /// }
891 ///
892 /// let position = Position { longitude: 1.987, latitude: 2.983 };
893 /// assert_eq!(format!("{position:?}"), "(1.987, 2.983)");
894 ///
895 /// assert_eq!(format!("{position:#?}"), "(
896 /// 1.987,
897 /// 2.983,
898 /// )");
899 /// ```
900 #[stable(feature = "rust1", since = "1.0.0")]
901 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
902}
903
904// Separate module to reexport the macro `Debug` from prelude without the trait `Debug`.
905pub(crate) mod macros {
906 /// Derive macro generating an impl of the trait `Debug`.
907 #[rustc_builtin_macro]
908 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
909 #[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive)]
910 pub macro Debug($item:item) {
911 /* compiler built-in */
912 }
913}
914#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
915#[doc(inline)]
916pub use macros::Debug;
917
918/// Format trait for an empty format, `{}`.
919///
920/// Implementing this trait for a type will automatically implement the
921/// [`ToString`][tostring] trait for the type, allowing the usage
922/// of the [`.to_string()`][tostring_function] method. Prefer implementing
923/// the `Display` trait for a type, rather than [`ToString`][tostring].
924///
925/// `Display` is similar to [`Debug`], but `Display` is for user-facing
926/// output, and so cannot be derived.
927///
928/// For more information on formatters, see [the module-level documentation][module].
929///
930/// [module]: ../../std/fmt/index.html
931/// [tostring]: ../../std/string/trait.ToString.html
932/// [tostring_function]: ../../std/string/trait.ToString.html#tymethod.to_string
933///
934/// # Internationalization
935///
936/// Because a type can only have one `Display` implementation, it is often preferable
937/// to only implement `Display` when there is a single most "obvious" way that
938/// values can be formatted as text. This could mean formatting according to the
939/// "invariant" culture and "undefined" locale, or it could mean that the type
940/// display is designed for a specific culture/locale, such as developer logs.
941///
942/// If not all values have a justifiably canonical textual format or if you want
943/// to support alternative formats not covered by the standard set of possible
944/// [formatting traits], the most flexible approach is display adapters: methods
945/// like [`str::escape_default`] or [`Path::display`] which create a wrapper
946/// implementing `Display` to output the specific display format.
947///
948/// [formatting traits]: ../../std/fmt/index.html#formatting-traits
949/// [`Path::display`]: ../../std/path/struct.Path.html#method.display
950///
951/// # Examples
952///
953/// Implementing `Display` on a type:
954///
955/// ```
956/// use std::fmt;
957///
958/// struct Point {
959/// x: i32,
960/// y: i32,
961/// }
962///
963/// impl fmt::Display for Point {
964/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
965/// write!(f, "({}, {})", self.x, self.y)
966/// }
967/// }
968///
969/// let origin = Point { x: 0, y: 0 };
970///
971/// assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");
972/// ```
973#[rustc_on_unimplemented(
974 on(
975 any(_Self = "std::path::Path", _Self = "std::path::PathBuf"),
976 label = "`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
977 note = "call `.display()` or `.to_string_lossy()` to safely print paths, \
978 as they may contain non-Unicode data"
979 ),
980 message = "`{Self}` doesn't implement `{Display}`",
981 label = "`{Self}` cannot be formatted with the default formatter",
982 note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead"
983)]
984#[doc(alias = "{}")]
985#[rustc_diagnostic_item = "Display"]
986#[stable(feature = "rust1", since = "1.0.0")]
987pub trait Display {
988 #[doc = include_str!("fmt_trait_method_doc.md")]
989 ///
990 /// # Examples
991 ///
992 /// ```
993 /// use std::fmt;
994 ///
995 /// struct Position {
996 /// longitude: f32,
997 /// latitude: f32,
998 /// }
999 ///
1000 /// impl fmt::Display for Position {
1001 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1002 /// write!(f, "({}, {})", self.longitude, self.latitude)
1003 /// }
1004 /// }
1005 ///
1006 /// assert_eq!(
1007 /// "(1.987, 2.983)",
1008 /// format!("{}", Position { longitude: 1.987, latitude: 2.983, }),
1009 /// );
1010 /// ```
1011 #[stable(feature = "rust1", since = "1.0.0")]
1012 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1013}
1014
1015/// `o` formatting.
1016///
1017/// The `Octal` trait should format its output as a number in base-8.
1018///
1019/// For primitive signed integers (`i8` to `i128`, and `isize`),
1020/// negative values are formatted as the two’s complement representation.
1021///
1022/// The alternate flag, `#`, adds a `0o` in front of the output.
1023///
1024/// For more information on formatters, see [the module-level documentation][module].
1025///
1026/// [module]: ../../std/fmt/index.html
1027///
1028/// # Examples
1029///
1030/// Basic usage with `i32`:
1031///
1032/// ```
1033/// let x = 42; // 42 is '52' in octal
1034///
1035/// assert_eq!(format!("{x:o}"), "52");
1036/// assert_eq!(format!("{x:#o}"), "0o52");
1037///
1038/// assert_eq!(format!("{:o}", -16), "37777777760");
1039/// ```
1040///
1041/// Implementing `Octal` on a type:
1042///
1043/// ```
1044/// use std::fmt;
1045///
1046/// struct Length(i32);
1047///
1048/// impl fmt::Octal for Length {
1049/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1050/// let val = self.0;
1051///
1052/// fmt::Octal::fmt(&val, f) // delegate to i32's implementation
1053/// }
1054/// }
1055///
1056/// let l = Length(9);
1057///
1058/// assert_eq!(format!("l as octal is: {l:o}"), "l as octal is: 11");
1059///
1060/// assert_eq!(format!("l as octal is: {l:#06o}"), "l as octal is: 0o0011");
1061/// ```
1062#[stable(feature = "rust1", since = "1.0.0")]
1063pub trait Octal {
1064 #[doc = include_str!("fmt_trait_method_doc.md")]
1065 #[stable(feature = "rust1", since = "1.0.0")]
1066 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1067}
1068
1069/// `b` formatting.
1070///
1071/// The `Binary` trait should format its output as a number in binary.
1072///
1073/// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]),
1074/// negative values are formatted as the two’s complement representation.
1075///
1076/// The alternate flag, `#`, adds a `0b` in front of the output.
1077///
1078/// For more information on formatters, see [the module-level documentation][module].
1079///
1080/// [module]: ../../std/fmt/index.html
1081///
1082/// # Examples
1083///
1084/// Basic usage with [`i32`]:
1085///
1086/// ```
1087/// let x = 42; // 42 is '101010' in binary
1088///
1089/// assert_eq!(format!("{x:b}"), "101010");
1090/// assert_eq!(format!("{x:#b}"), "0b101010");
1091///
1092/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
1093/// ```
1094///
1095/// Implementing `Binary` on a type:
1096///
1097/// ```
1098/// use std::fmt;
1099///
1100/// struct Length(i32);
1101///
1102/// impl fmt::Binary for Length {
1103/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1104/// let val = self.0;
1105///
1106/// fmt::Binary::fmt(&val, f) // delegate to i32's implementation
1107/// }
1108/// }
1109///
1110/// let l = Length(107);
1111///
1112/// assert_eq!(format!("l as binary is: {l:b}"), "l as binary is: 1101011");
1113///
1114/// assert_eq!(
1115/// // Note that the `0b` prefix added by `#` is included in the total width, so we
1116/// // need to add two to correctly display all 32 bits.
1117/// format!("l as binary is: {l:#034b}"),
1118/// "l as binary is: 0b00000000000000000000000001101011"
1119/// );
1120/// ```
1121#[stable(feature = "rust1", since = "1.0.0")]
1122pub trait Binary {
1123 #[doc = include_str!("fmt_trait_method_doc.md")]
1124 #[stable(feature = "rust1", since = "1.0.0")]
1125 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1126}
1127
1128/// `x` formatting.
1129///
1130/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
1131/// in lower case.
1132///
1133/// For primitive signed integers (`i8` to `i128`, and `isize`),
1134/// negative values are formatted as the two’s complement representation.
1135///
1136/// The alternate flag, `#`, adds a `0x` in front of the output.
1137///
1138/// For more information on formatters, see [the module-level documentation][module].
1139///
1140/// [module]: ../../std/fmt/index.html
1141///
1142/// # Examples
1143///
1144/// Basic usage with `i32`:
1145///
1146/// ```
1147/// let y = 42; // 42 is '2a' in hex
1148///
1149/// assert_eq!(format!("{y:x}"), "2a");
1150/// assert_eq!(format!("{y:#x}"), "0x2a");
1151///
1152/// assert_eq!(format!("{:x}", -16), "fffffff0");
1153/// ```
1154///
1155/// Implementing `LowerHex` on a type:
1156///
1157/// ```
1158/// use std::fmt;
1159///
1160/// struct Length(i32);
1161///
1162/// impl fmt::LowerHex for Length {
1163/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1164/// let val = self.0;
1165///
1166/// fmt::LowerHex::fmt(&val, f) // delegate to i32's implementation
1167/// }
1168/// }
1169///
1170/// let l = Length(9);
1171///
1172/// assert_eq!(format!("l as hex is: {l:x}"), "l as hex is: 9");
1173///
1174/// assert_eq!(format!("l as hex is: {l:#010x}"), "l as hex is: 0x00000009");
1175/// ```
1176#[stable(feature = "rust1", since = "1.0.0")]
1177pub trait LowerHex {
1178 #[doc = include_str!("fmt_trait_method_doc.md")]
1179 #[stable(feature = "rust1", since = "1.0.0")]
1180 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1181}
1182
1183/// `X` formatting.
1184///
1185/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
1186/// in upper case.
1187///
1188/// For primitive signed integers (`i8` to `i128`, and `isize`),
1189/// negative values are formatted as the two’s complement representation.
1190///
1191/// The alternate flag, `#`, adds a `0x` in front of the output.
1192///
1193/// For more information on formatters, see [the module-level documentation][module].
1194///
1195/// [module]: ../../std/fmt/index.html
1196///
1197/// # Examples
1198///
1199/// Basic usage with `i32`:
1200///
1201/// ```
1202/// let y = 42; // 42 is '2A' in hex
1203///
1204/// assert_eq!(format!("{y:X}"), "2A");
1205/// assert_eq!(format!("{y:#X}"), "0x2A");
1206///
1207/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
1208/// ```
1209///
1210/// Implementing `UpperHex` on a type:
1211///
1212/// ```
1213/// use std::fmt;
1214///
1215/// struct Length(i32);
1216///
1217/// impl fmt::UpperHex for Length {
1218/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1219/// let val = self.0;
1220///
1221/// fmt::UpperHex::fmt(&val, f) // delegate to i32's implementation
1222/// }
1223/// }
1224///
1225/// let l = Length(i32::MAX);
1226///
1227/// assert_eq!(format!("l as hex is: {l:X}"), "l as hex is: 7FFFFFFF");
1228///
1229/// assert_eq!(format!("l as hex is: {l:#010X}"), "l as hex is: 0x7FFFFFFF");
1230/// ```
1231#[stable(feature = "rust1", since = "1.0.0")]
1232pub trait UpperHex {
1233 #[doc = include_str!("fmt_trait_method_doc.md")]
1234 #[stable(feature = "rust1", since = "1.0.0")]
1235 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1236}
1237
1238/// `p` formatting.
1239///
1240/// The `Pointer` trait should format its output as a memory location. This is commonly presented
1241/// as hexadecimal. For more information on formatters, see [the module-level documentation][module].
1242///
1243/// Printing of pointers is not a reliable way to discover how Rust programs are implemented.
1244/// The act of reading an address changes the program itself, and may change how the data is represented
1245/// in memory, and may affect which optimizations are applied to the code.
1246///
1247/// The printed pointer values are not guaranteed to be stable nor unique identifiers of objects.
1248/// Rust allows moving values to different memory locations, and may reuse the same memory locations
1249/// for different purposes.
1250///
1251/// There is no guarantee that the printed value can be converted back to a pointer.
1252///
1253/// [module]: ../../std/fmt/index.html
1254///
1255/// # Examples
1256///
1257/// Basic usage with `&i32`:
1258///
1259/// ```
1260/// let x = &42;
1261///
1262/// let address = format!("{x:p}"); // this produces something like '0x7f06092ac6d0'
1263/// ```
1264///
1265/// Implementing `Pointer` on a type:
1266///
1267/// ```
1268/// use std::fmt;
1269///
1270/// struct Length(i32);
1271///
1272/// impl fmt::Pointer for Length {
1273/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1274/// // use `as` to convert to a `*const T`, which implements Pointer, which we can use
1275///
1276/// let ptr = self as *const Self;
1277/// fmt::Pointer::fmt(&ptr, f)
1278/// }
1279/// }
1280///
1281/// let l = Length(42);
1282///
1283/// println!("l is in memory here: {l:p}");
1284///
1285/// let l_ptr = format!("{l:018p}");
1286/// assert_eq!(l_ptr.len(), 18);
1287/// assert_eq!(&l_ptr[..2], "0x");
1288/// ```
1289#[stable(feature = "rust1", since = "1.0.0")]
1290#[rustc_diagnostic_item = "Pointer"]
1291pub trait Pointer {
1292 #[doc = include_str!("fmt_trait_method_doc.md")]
1293 #[stable(feature = "rust1", since = "1.0.0")]
1294 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1295}
1296
1297/// `e` formatting.
1298///
1299/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
1300///
1301/// For more information on formatters, see [the module-level documentation][module].
1302///
1303/// [module]: ../../std/fmt/index.html
1304///
1305/// # Examples
1306///
1307/// Basic usage with `f64`:
1308///
1309/// ```
1310/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
1311///
1312/// assert_eq!(format!("{x:e}"), "4.2e1");
1313/// ```
1314///
1315/// Implementing `LowerExp` on a type:
1316///
1317/// ```
1318/// use std::fmt;
1319///
1320/// struct Length(i32);
1321///
1322/// impl fmt::LowerExp for Length {
1323/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1324/// let val = f64::from(self.0);
1325/// fmt::LowerExp::fmt(&val, f) // delegate to f64's implementation
1326/// }
1327/// }
1328///
1329/// let l = Length(100);
1330///
1331/// assert_eq!(
1332/// format!("l in scientific notation is: {l:e}"),
1333/// "l in scientific notation is: 1e2"
1334/// );
1335///
1336/// assert_eq!(
1337/// format!("l in scientific notation is: {l:05e}"),
1338/// "l in scientific notation is: 001e2"
1339/// );
1340/// ```
1341#[stable(feature = "rust1", since = "1.0.0")]
1342pub trait LowerExp {
1343 #[doc = include_str!("fmt_trait_method_doc.md")]
1344 #[stable(feature = "rust1", since = "1.0.0")]
1345 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1346}
1347
1348/// `E` formatting.
1349///
1350/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
1351///
1352/// For more information on formatters, see [the module-level documentation][module].
1353///
1354/// [module]: ../../std/fmt/index.html
1355///
1356/// # Examples
1357///
1358/// Basic usage with `f64`:
1359///
1360/// ```
1361/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
1362///
1363/// assert_eq!(format!("{x:E}"), "4.2E1");
1364/// ```
1365///
1366/// Implementing `UpperExp` on a type:
1367///
1368/// ```
1369/// use std::fmt;
1370///
1371/// struct Length(i32);
1372///
1373/// impl fmt::UpperExp for Length {
1374/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1375/// let val = f64::from(self.0);
1376/// fmt::UpperExp::fmt(&val, f) // delegate to f64's implementation
1377/// }
1378/// }
1379///
1380/// let l = Length(100);
1381///
1382/// assert_eq!(
1383/// format!("l in scientific notation is: {l:E}"),
1384/// "l in scientific notation is: 1E2"
1385/// );
1386///
1387/// assert_eq!(
1388/// format!("l in scientific notation is: {l:05E}"),
1389/// "l in scientific notation is: 001E2"
1390/// );
1391/// ```
1392#[stable(feature = "rust1", since = "1.0.0")]
1393pub trait UpperExp {
1394 #[doc = include_str!("fmt_trait_method_doc.md")]
1395 #[stable(feature = "rust1", since = "1.0.0")]
1396 fn fmt(&self, f: &mut Formatter<'_>) -> Result;
1397}
1398
1399/// Takes an output stream and an `Arguments` struct that can be precompiled with
1400/// the `format_args!` macro.
1401///
1402/// The arguments will be formatted according to the specified format string
1403/// into the output stream provided.
1404///
1405/// # Examples
1406///
1407/// Basic usage:
1408///
1409/// ```
1410/// use std::fmt;
1411///
1412/// let mut output = String::new();
1413/// fmt::write(&mut output, format_args!("Hello {}!", "world"))
1414/// .expect("Error occurred while trying to write in String");
1415/// assert_eq!(output, "Hello world!");
1416/// ```
1417///
1418/// Please note that using [`write!`] might be preferable. Example:
1419///
1420/// ```
1421/// use std::fmt::Write;
1422///
1423/// let mut output = String::new();
1424/// write!(&mut output, "Hello {}!", "world")
1425/// .expect("Error occurred while trying to write in String");
1426/// assert_eq!(output, "Hello world!");
1427/// ```
1428///
1429/// [`write!`]: crate::write!
1430#[stable(feature = "rust1", since = "1.0.0")]
1431pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
1432 let mut formatter = Formatter::new(output, FormattingOptions::new());
1433 let mut idx = 0;
1434
1435 match args.fmt {
1436 None => {
1437 // We can use default formatting parameters for all arguments.
1438 for (i, arg) in args.args.iter().enumerate() {
1439 // SAFETY: args.args and args.pieces come from the same Arguments,
1440 // which guarantees the indexes are always within bounds.
1441 let piece = unsafe { args.pieces.get_unchecked(i) };
1442 if !piece.is_empty() {
1443 formatter.buf.write_str(*piece)?;
1444 }
1445
1446 // SAFETY: There are no formatting parameters and hence no
1447 // count arguments.
1448 unsafe {
1449 arg.fmt(&mut formatter)?;
1450 }
1451 idx += 1;
1452 }
1453 }
1454 Some(fmt) => {
1455 // Every spec has a corresponding argument that is preceded by
1456 // a string piece.
1457 for (i, arg) in fmt.iter().enumerate() {
1458 // SAFETY: fmt and args.pieces come from the same Arguments,
1459 // which guarantees the indexes are always within bounds.
1460 let piece = unsafe { args.pieces.get_unchecked(i) };
1461 if !piece.is_empty() {
1462 formatter.buf.write_str(*piece)?;
1463 }
1464 // SAFETY: arg and args.args come from the same Arguments,
1465 // which guarantees the indexes are always within bounds.
1466 unsafe { run(&mut formatter, arg, args.args) }?;
1467 idx += 1;
1468 }
1469 }
1470 }
1471
1472 // There can be only one trailing string piece left.
1473 if let Some(piece) = args.pieces.get(idx) {
1474 formatter.buf.write_str(*piece)?;
1475 }
1476
1477 Ok(())
1478}
1479
1480unsafe fn run(fmt: &mut Formatter<'_>, arg: &rt::Placeholder, args: &[rt::Argument<'_>]) -> Result {
1481 fmt.options.fill = arg.fill;
1482 fmt.options.align = arg.align.into();
1483 fmt.options.flags = arg.flags;
1484 // SAFETY: arg and args come from the same Arguments,
1485 // which guarantees the indexes are always within bounds.
1486 unsafe {
1487 fmt.options.width = getcount(args, &arg.width);
1488 fmt.options.precision = getcount(args, &arg.precision);
1489 }
1490
1491 // Extract the correct argument
1492 debug_assert!(arg.position < args.len());
1493 // SAFETY: arg and args come from the same Arguments,
1494 // which guarantees its index is always within bounds.
1495 let value = unsafe { args.get_unchecked(arg.position) };
1496
1497 // Then actually do some printing
1498 // SAFETY: this is a placeholder argument.
1499 unsafe { value.fmt(fmt) }
1500}
1501
1502unsafe fn getcount(args: &[rt::Argument<'_>], cnt: &rt::Count) -> Option<u16> {
1503 match *cnt {
1504 #[cfg(bootstrap)]
1505 rt::Count::Is(n) => Some(n as u16),
1506 #[cfg(not(bootstrap))]
1507 rt::Count::Is(n) => Some(n),
1508 rt::Count::Implied => None,
1509 rt::Count::Param(i) => {
1510 debug_assert!(i < args.len());
1511 // SAFETY: cnt and args come from the same Arguments,
1512 // which guarantees this index is always within bounds.
1513 unsafe { args.get_unchecked(i).as_u16() }
1514 }
1515 }
1516}
1517
1518/// Padding after the end of something. Returned by `Formatter::padding`.
1519#[must_use = "don't forget to write the post padding"]
1520pub(crate) struct PostPadding {
1521 fill: char,
1522 padding: u16,
1523}
1524
1525impl PostPadding {
1526 fn new(fill: char, padding: u16) -> PostPadding {
1527 PostPadding { fill, padding }
1528 }
1529
1530 /// Writes this post padding.
1531 pub(crate) fn write(self, f: &mut Formatter<'_>) -> Result {
1532 for _ in 0..self.padding {
1533 f.buf.write_char(self.fill)?;
1534 }
1535 Ok(())
1536 }
1537}
1538
1539impl<'a> Formatter<'a> {
1540 fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
1541 where
1542 'b: 'c,
1543 F: FnOnce(&'b mut (dyn Write + 'b)) -> &'c mut (dyn Write + 'c),
1544 {
1545 Formatter {
1546 // We want to change this
1547 buf: wrap(self.buf),
1548
1549 // And preserve these
1550 options: self.options,
1551 }
1552 }
1553
1554 // Helper methods used for padding and processing formatting arguments that
1555 // all formatting traits can use.
1556
1557 /// Performs the correct padding for an integer which has already been
1558 /// emitted into a str. The str should *not* contain the sign for the
1559 /// integer, that will be added by this method.
1560 ///
1561 /// # Arguments
1562 ///
1563 /// * is_nonnegative - whether the original integer was either positive or zero.
1564 /// * prefix - if the '#' character (Alternate) is provided, this
1565 /// is the prefix to put in front of the number.
1566 /// * buf - the byte array that the number has been formatted into
1567 ///
1568 /// This function will correctly account for the flags provided as well as
1569 /// the minimum width. It will not take precision into account.
1570 ///
1571 /// # Examples
1572 ///
1573 /// ```
1574 /// use std::fmt;
1575 ///
1576 /// struct Foo { nb: i32 }
1577 ///
1578 /// impl Foo {
1579 /// fn new(nb: i32) -> Foo {
1580 /// Foo {
1581 /// nb,
1582 /// }
1583 /// }
1584 /// }
1585 ///
1586 /// impl fmt::Display for Foo {
1587 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1588 /// // We need to remove "-" from the number output.
1589 /// let tmp = self.nb.abs().to_string();
1590 ///
1591 /// formatter.pad_integral(self.nb >= 0, "Foo ", &tmp)
1592 /// }
1593 /// }
1594 ///
1595 /// assert_eq!(format!("{}", Foo::new(2)), "2");
1596 /// assert_eq!(format!("{}", Foo::new(-1)), "-1");
1597 /// assert_eq!(format!("{}", Foo::new(0)), "0");
1598 /// assert_eq!(format!("{:#}", Foo::new(-1)), "-Foo 1");
1599 /// assert_eq!(format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
1600 /// ```
1601 #[stable(feature = "rust1", since = "1.0.0")]
1602 pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
1603 let mut width = buf.len();
1604
1605 let mut sign = None;
1606 if !is_nonnegative {
1607 sign = Some('-');
1608 width += 1;
1609 } else if self.sign_plus() {
1610 sign = Some('+');
1611 width += 1;
1612 }
1613
1614 let prefix = if self.alternate() {
1615 width += prefix.chars().count();
1616 Some(prefix)
1617 } else {
1618 None
1619 };
1620
1621 // Writes the sign if it exists, and then the prefix if it was requested
1622 #[inline(never)]
1623 fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result {
1624 if let Some(c) = sign {
1625 f.buf.write_char(c)?;
1626 }
1627 if let Some(prefix) = prefix { f.buf.write_str(prefix) } else { Ok(()) }
1628 }
1629
1630 // The `width` field is more of a `min-width` parameter at this point.
1631 match self.options.width {
1632 // If there's no minimum length requirements then we can just
1633 // write the bytes.
1634 None => {
1635 write_prefix(self, sign, prefix)?;
1636 self.buf.write_str(buf)
1637 }
1638 // Check if we're over the minimum width, if so then we can also
1639 // just write the bytes.
1640 Some(min) if width >= usize::from(min) => {
1641 write_prefix(self, sign, prefix)?;
1642 self.buf.write_str(buf)
1643 }
1644 // The sign and prefix goes before the padding if the fill character
1645 // is zero
1646 Some(min) if self.sign_aware_zero_pad() => {
1647 let old_fill = crate::mem::replace(&mut self.options.fill, '0');
1648 let old_align =
1649 crate::mem::replace(&mut self.options.align, Some(Alignment::Right));
1650 write_prefix(self, sign, prefix)?;
1651 let post_padding = self.padding(min - width as u16, Alignment::Right)?;
1652 self.buf.write_str(buf)?;
1653 post_padding.write(self)?;
1654 self.options.fill = old_fill;
1655 self.options.align = old_align;
1656 Ok(())
1657 }
1658 // Otherwise, the sign and prefix goes after the padding
1659 Some(min) => {
1660 let post_padding = self.padding(min - width as u16, Alignment::Right)?;
1661 write_prefix(self, sign, prefix)?;
1662 self.buf.write_str(buf)?;
1663 post_padding.write(self)
1664 }
1665 }
1666 }
1667
1668 /// Takes a string slice and emits it to the internal buffer after applying
1669 /// the relevant formatting flags specified.
1670 ///
1671 /// The flags recognized for generic strings are:
1672 ///
1673 /// * width - the minimum width of what to emit
1674 /// * fill/align - what to emit and where to emit it if the string
1675 /// provided needs to be padded
1676 /// * precision - the maximum length to emit, the string is truncated if it
1677 /// is longer than this length
1678 ///
1679 /// Notably this function ignores the `flag` parameters.
1680 ///
1681 /// # Examples
1682 ///
1683 /// ```
1684 /// use std::fmt;
1685 ///
1686 /// struct Foo;
1687 ///
1688 /// impl fmt::Display for Foo {
1689 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1690 /// formatter.pad("Foo")
1691 /// }
1692 /// }
1693 ///
1694 /// assert_eq!(format!("{Foo:<4}"), "Foo ");
1695 /// assert_eq!(format!("{Foo:0>4}"), "0Foo");
1696 /// ```
1697 #[stable(feature = "rust1", since = "1.0.0")]
1698 pub fn pad(&mut self, s: &str) -> Result {
1699 // Make sure there's a fast path up front.
1700 if self.options.width.is_none() && self.options.precision.is_none() {
1701 return self.buf.write_str(s);
1702 }
1703
1704 // The `precision` field can be interpreted as a maximum width for the
1705 // string being formatted.
1706 let (s, char_count) = if let Some(max_char_count) = self.options.precision {
1707 let mut iter = s.char_indices();
1708 let remaining = match iter.advance_by(usize::from(max_char_count)) {
1709 Ok(()) => 0,
1710 Err(remaining) => remaining.get(),
1711 };
1712 // SAFETY: The offset of `.char_indices()` is guaranteed to be
1713 // in-bounds and between character boundaries.
1714 let truncated = unsafe { s.get_unchecked(..iter.offset()) };
1715 (truncated, usize::from(max_char_count) - remaining)
1716 } else {
1717 // Use the optimized char counting algorithm for the full string.
1718 (s, s.chars().count())
1719 };
1720
1721 // The `width` field is more of a minimum width parameter at this point.
1722 if let Some(width) = self.options.width
1723 && char_count < usize::from(width)
1724 {
1725 // If we're under the minimum width, then fill up the minimum width
1726 // with the specified string + some alignment.
1727 let post_padding = self.padding(width - char_count as u16, Alignment::Left)?;
1728 self.buf.write_str(s)?;
1729 post_padding.write(self)
1730 } else {
1731 // If we're over the minimum width or there is no minimum width, we
1732 // can just emit the string.
1733 self.buf.write_str(s)
1734 }
1735 }
1736
1737 /// Writes the pre-padding and returns the unwritten post-padding.
1738 ///
1739 /// Callers are responsible for ensuring post-padding is written after the
1740 /// thing that is being padded.
1741 pub(crate) fn padding(
1742 &mut self,
1743 padding: u16,
1744 default: Alignment,
1745 ) -> result::Result<PostPadding, Error> {
1746 let align = self.align().unwrap_or(default);
1747
1748 let (pre_pad, post_pad) = match align {
1749 Alignment::Left => (0, padding),
1750 Alignment::Right => (padding, 0),
1751 Alignment::Center => (padding / 2, (padding + 1) / 2),
1752 };
1753
1754 for _ in 0..pre_pad {
1755 self.buf.write_char(self.options.fill)?;
1756 }
1757
1758 Ok(PostPadding::new(self.options.fill, post_pad))
1759 }
1760
1761 /// Takes the formatted parts and applies the padding.
1762 ///
1763 /// Assumes that the caller already has rendered the parts with required precision,
1764 /// so that `self.precision` can be ignored.
1765 ///
1766 /// # Safety
1767 ///
1768 /// Any `numfmt::Part::Copy` parts in `formatted` must contain valid UTF-8.
1769 unsafe fn pad_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
1770 if let Some(mut width) = self.options.width {
1771 // for the sign-aware zero padding, we render the sign first and
1772 // behave as if we had no sign from the beginning.
1773 let mut formatted = formatted.clone();
1774 let old_fill = self.options.fill;
1775 let old_align = self.options.align;
1776 if self.sign_aware_zero_pad() {
1777 // a sign always goes first
1778 let sign = formatted.sign;
1779 self.buf.write_str(sign)?;
1780
1781 // remove the sign from the formatted parts
1782 formatted.sign = "";
1783 width = width.saturating_sub(sign.len() as u16);
1784 self.options.fill = '0';
1785 self.options.align = Some(Alignment::Right);
1786 }
1787
1788 // remaining parts go through the ordinary padding process.
1789 let len = formatted.len();
1790 let ret = if usize::from(width) <= len {
1791 // no padding
1792 // SAFETY: Per the precondition.
1793 unsafe { self.write_formatted_parts(&formatted) }
1794 } else {
1795 let post_padding = self.padding(width - len as u16, Alignment::Right)?;
1796 // SAFETY: Per the precondition.
1797 unsafe {
1798 self.write_formatted_parts(&formatted)?;
1799 }
1800 post_padding.write(self)
1801 };
1802 self.options.fill = old_fill;
1803 self.options.align = old_align;
1804 ret
1805 } else {
1806 // this is the common case and we take a shortcut
1807 // SAFETY: Per the precondition.
1808 unsafe { self.write_formatted_parts(formatted) }
1809 }
1810 }
1811
1812 /// # Safety
1813 ///
1814 /// Any `numfmt::Part::Copy` parts in `formatted` must contain valid UTF-8.
1815 unsafe fn write_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
1816 unsafe fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
1817 // SAFETY: This is used for `numfmt::Part::Num` and `numfmt::Part::Copy`.
1818 // It's safe to use for `numfmt::Part::Num` since every char `c` is between
1819 // `b'0'` and `b'9'`, which means `s` is valid UTF-8. It's safe to use for
1820 // `numfmt::Part::Copy` due to this function's precondition.
1821 buf.write_str(unsafe { str::from_utf8_unchecked(s) })
1822 }
1823
1824 if !formatted.sign.is_empty() {
1825 self.buf.write_str(formatted.sign)?;
1826 }
1827 for part in formatted.parts {
1828 match *part {
1829 numfmt::Part::Zero(mut nzeroes) => {
1830 const ZEROES: &str = // 64 zeroes
1831 "0000000000000000000000000000000000000000000000000000000000000000";
1832 while nzeroes > ZEROES.len() {
1833 self.buf.write_str(ZEROES)?;
1834 nzeroes -= ZEROES.len();
1835 }
1836 if nzeroes > 0 {
1837 self.buf.write_str(&ZEROES[..nzeroes])?;
1838 }
1839 }
1840 numfmt::Part::Num(mut v) => {
1841 let mut s = [0; 5];
1842 let len = part.len();
1843 for c in s[..len].iter_mut().rev() {
1844 *c = b'0' + (v % 10) as u8;
1845 v /= 10;
1846 }
1847 // SAFETY: Per the precondition.
1848 unsafe {
1849 write_bytes(self.buf, &s[..len])?;
1850 }
1851 }
1852 // SAFETY: Per the precondition.
1853 numfmt::Part::Copy(buf) => unsafe {
1854 write_bytes(self.buf, buf)?;
1855 },
1856 }
1857 }
1858 Ok(())
1859 }
1860
1861 /// Writes some data to the underlying buffer contained within this
1862 /// formatter.
1863 ///
1864 /// # Examples
1865 ///
1866 /// ```
1867 /// use std::fmt;
1868 ///
1869 /// struct Foo;
1870 ///
1871 /// impl fmt::Display for Foo {
1872 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1873 /// formatter.write_str("Foo")
1874 /// // This is equivalent to:
1875 /// // write!(formatter, "Foo")
1876 /// }
1877 /// }
1878 ///
1879 /// assert_eq!(format!("{Foo}"), "Foo");
1880 /// assert_eq!(format!("{Foo:0>8}"), "Foo");
1881 /// ```
1882 #[stable(feature = "rust1", since = "1.0.0")]
1883 pub fn write_str(&mut self, data: &str) -> Result {
1884 self.buf.write_str(data)
1885 }
1886
1887 /// Glue for usage of the [`write!`] macro with implementors of this trait.
1888 ///
1889 /// This method should generally not be invoked manually, but rather through
1890 /// the [`write!`] macro itself.
1891 ///
1892 /// Writes some formatted information into this instance.
1893 ///
1894 /// # Examples
1895 ///
1896 /// ```
1897 /// use std::fmt;
1898 ///
1899 /// struct Foo(i32);
1900 ///
1901 /// impl fmt::Display for Foo {
1902 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1903 /// formatter.write_fmt(format_args!("Foo {}", self.0))
1904 /// }
1905 /// }
1906 ///
1907 /// assert_eq!(format!("{}", Foo(-1)), "Foo -1");
1908 /// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
1909 /// ```
1910 #[stable(feature = "rust1", since = "1.0.0")]
1911 #[inline]
1912 pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
1913 if let Some(s) = fmt.as_statically_known_str() {
1914 self.buf.write_str(s)
1915 } else {
1916 write(self.buf, fmt)
1917 }
1918 }
1919
1920 /// Returns flags for formatting.
1921 #[must_use]
1922 #[stable(feature = "rust1", since = "1.0.0")]
1923 #[deprecated(
1924 since = "1.24.0",
1925 note = "use the `sign_plus`, `sign_minus`, `alternate`, \
1926 or `sign_aware_zero_pad` methods instead"
1927 )]
1928 pub fn flags(&self) -> u32 {
1929 self.options.flags
1930 }
1931
1932 /// Returns the character used as 'fill' whenever there is alignment.
1933 ///
1934 /// # Examples
1935 ///
1936 /// ```
1937 /// use std::fmt;
1938 ///
1939 /// struct Foo;
1940 ///
1941 /// impl fmt::Display for Foo {
1942 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1943 /// let c = formatter.fill();
1944 /// if let Some(width) = formatter.width() {
1945 /// for _ in 0..width {
1946 /// write!(formatter, "{c}")?;
1947 /// }
1948 /// Ok(())
1949 /// } else {
1950 /// write!(formatter, "{c}")
1951 /// }
1952 /// }
1953 /// }
1954 ///
1955 /// // We set alignment to the right with ">".
1956 /// assert_eq!(format!("{Foo:G>3}"), "GGG");
1957 /// assert_eq!(format!("{Foo:t>6}"), "tttttt");
1958 /// ```
1959 #[must_use]
1960 #[stable(feature = "fmt_flags", since = "1.5.0")]
1961 pub fn fill(&self) -> char {
1962 self.options.fill
1963 }
1964
1965 /// Returns a flag indicating what form of alignment was requested.
1966 ///
1967 /// # Examples
1968 ///
1969 /// ```
1970 /// use std::fmt::{self, Alignment};
1971 ///
1972 /// struct Foo;
1973 ///
1974 /// impl fmt::Display for Foo {
1975 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
1976 /// let s = if let Some(s) = formatter.align() {
1977 /// match s {
1978 /// Alignment::Left => "left",
1979 /// Alignment::Right => "right",
1980 /// Alignment::Center => "center",
1981 /// }
1982 /// } else {
1983 /// "into the void"
1984 /// };
1985 /// write!(formatter, "{s}")
1986 /// }
1987 /// }
1988 ///
1989 /// assert_eq!(format!("{Foo:<}"), "left");
1990 /// assert_eq!(format!("{Foo:>}"), "right");
1991 /// assert_eq!(format!("{Foo:^}"), "center");
1992 /// assert_eq!(format!("{Foo}"), "into the void");
1993 /// ```
1994 #[must_use]
1995 #[stable(feature = "fmt_flags_align", since = "1.28.0")]
1996 pub fn align(&self) -> Option<Alignment> {
1997 self.options.align
1998 }
1999
2000 /// Returns the optionally specified integer width that the output should be.
2001 ///
2002 /// # Examples
2003 ///
2004 /// ```
2005 /// use std::fmt;
2006 ///
2007 /// struct Foo(i32);
2008 ///
2009 /// impl fmt::Display for Foo {
2010 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
2011 /// if let Some(width) = formatter.width() {
2012 /// // If we received a width, we use it
2013 /// write!(formatter, "{:width$}", format!("Foo({})", self.0), width = width)
2014 /// } else {
2015 /// // Otherwise we do nothing special
2016 /// write!(formatter, "Foo({})", self.0)
2017 /// }
2018 /// }
2019 /// }
2020 ///
2021 /// assert_eq!(format!("{:10}", Foo(23)), "Foo(23) ");
2022 /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
2023 /// ```
2024 #[must_use]
2025 #[stable(feature = "fmt_flags", since = "1.5.0")]
2026 pub fn width(&self) -> Option<usize> {
2027 self.options.width.map(|x| x as usize)
2028 }
2029
2030 /// Returns the optionally specified precision for numeric types.
2031 /// Alternatively, the maximum width for string types.
2032 ///
2033 /// # Examples
2034 ///
2035 /// ```
2036 /// use std::fmt;
2037 ///
2038 /// struct Foo(f32);
2039 ///
2040 /// impl fmt::Display for Foo {
2041 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
2042 /// if let Some(precision) = formatter.precision() {
2043 /// // If we received a precision, we use it.
2044 /// write!(formatter, "Foo({1:.*})", precision, self.0)
2045 /// } else {
2046 /// // Otherwise we default to 2.
2047 /// write!(formatter, "Foo({:.2})", self.0)
2048 /// }
2049 /// }
2050 /// }
2051 ///
2052 /// assert_eq!(format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
2053 /// assert_eq!(format!("{}", Foo(23.2)), "Foo(23.20)");
2054 /// ```
2055 #[must_use]
2056 #[stable(feature = "fmt_flags", since = "1.5.0")]
2057 pub fn precision(&self) -> Option<usize> {
2058 self.options.precision.map(|x| x as usize)
2059 }
2060
2061 /// Determines if the `+` flag was specified.
2062 ///
2063 /// # Examples
2064 ///
2065 /// ```
2066 /// use std::fmt;
2067 ///
2068 /// struct Foo(i32);
2069 ///
2070 /// impl fmt::Display for Foo {
2071 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
2072 /// if formatter.sign_plus() {
2073 /// write!(formatter,
2074 /// "Foo({}{})",
2075 /// if self.0 < 0 { '-' } else { '+' },
2076 /// self.0.abs())
2077 /// } else {
2078 /// write!(formatter, "Foo({})", self.0)
2079 /// }
2080 /// }
2081 /// }
2082 ///
2083 /// assert_eq!(format!("{:+}", Foo(23)), "Foo(+23)");
2084 /// assert_eq!(format!("{:+}", Foo(-23)), "Foo(-23)");
2085 /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
2086 /// ```
2087 #[must_use]
2088 #[stable(feature = "fmt_flags", since = "1.5.0")]
2089 pub fn sign_plus(&self) -> bool {
2090 self.options.flags & (1 << rt::Flag::SignPlus as u32) != 0
2091 }
2092
2093 /// Determines if the `-` flag was specified.
2094 ///
2095 /// # Examples
2096 ///
2097 /// ```
2098 /// use std::fmt;
2099 ///
2100 /// struct Foo(i32);
2101 ///
2102 /// impl fmt::Display for Foo {
2103 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
2104 /// if formatter.sign_minus() {
2105 /// // You want a minus sign? Have one!
2106 /// write!(formatter, "-Foo({})", self.0)
2107 /// } else {
2108 /// write!(formatter, "Foo({})", self.0)
2109 /// }
2110 /// }
2111 /// }
2112 ///
2113 /// assert_eq!(format!("{:-}", Foo(23)), "-Foo(23)");
2114 /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
2115 /// ```
2116 #[must_use]
2117 #[stable(feature = "fmt_flags", since = "1.5.0")]
2118 pub fn sign_minus(&self) -> bool {
2119 self.options.flags & (1 << rt::Flag::SignMinus as u32) != 0
2120 }
2121
2122 /// Determines if the `#` flag was specified.
2123 ///
2124 /// # Examples
2125 ///
2126 /// ```
2127 /// use std::fmt;
2128 ///
2129 /// struct Foo(i32);
2130 ///
2131 /// impl fmt::Display for Foo {
2132 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
2133 /// if formatter.alternate() {
2134 /// write!(formatter, "Foo({})", self.0)
2135 /// } else {
2136 /// write!(formatter, "{}", self.0)
2137 /// }
2138 /// }
2139 /// }
2140 ///
2141 /// assert_eq!(format!("{:#}", Foo(23)), "Foo(23)");
2142 /// assert_eq!(format!("{}", Foo(23)), "23");
2143 /// ```
2144 #[must_use]
2145 #[stable(feature = "fmt_flags", since = "1.5.0")]
2146 pub fn alternate(&self) -> bool {
2147 self.options.flags & (1 << rt::Flag::Alternate as u32) != 0
2148 }
2149
2150 /// Determines if the `0` flag was specified.
2151 ///
2152 /// # Examples
2153 ///
2154 /// ```
2155 /// use std::fmt;
2156 ///
2157 /// struct Foo(i32);
2158 ///
2159 /// impl fmt::Display for Foo {
2160 /// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
2161 /// assert!(formatter.sign_aware_zero_pad());
2162 /// assert_eq!(formatter.width(), Some(4));
2163 /// // We ignore the formatter's options.
2164 /// write!(formatter, "{}", self.0)
2165 /// }
2166 /// }
2167 ///
2168 /// assert_eq!(format!("{:04}", Foo(23)), "23");
2169 /// ```
2170 #[must_use]
2171 #[stable(feature = "fmt_flags", since = "1.5.0")]
2172 pub fn sign_aware_zero_pad(&self) -> bool {
2173 self.options.flags & (1 << rt::Flag::SignAwareZeroPad as u32) != 0
2174 }
2175
2176 // FIXME: Decide what public API we want for these two flags.
2177 // https://github.com/rust-lang/rust/issues/48584
2178 fn debug_lower_hex(&self) -> bool {
2179 self.options.flags & (1 << rt::Flag::DebugLowerHex as u32) != 0
2180 }
2181
2182 fn debug_upper_hex(&self) -> bool {
2183 self.options.flags & (1 << rt::Flag::DebugUpperHex as u32) != 0
2184 }
2185
2186 /// Creates a [`DebugStruct`] builder designed to assist with creation of
2187 /// [`fmt::Debug`] implementations for structs.
2188 ///
2189 /// [`fmt::Debug`]: self::Debug
2190 ///
2191 /// # Examples
2192 ///
2193 /// ```rust
2194 /// use std::fmt;
2195 /// use std::net::Ipv4Addr;
2196 ///
2197 /// struct Foo {
2198 /// bar: i32,
2199 /// baz: String,
2200 /// addr: Ipv4Addr,
2201 /// }
2202 ///
2203 /// impl fmt::Debug for Foo {
2204 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2205 /// fmt.debug_struct("Foo")
2206 /// .field("bar", &self.bar)
2207 /// .field("baz", &self.baz)
2208 /// .field("addr", &format_args!("{}", self.addr))
2209 /// .finish()
2210 /// }
2211 /// }
2212 ///
2213 /// assert_eq!(
2214 /// "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
2215 /// format!("{:?}", Foo {
2216 /// bar: 10,
2217 /// baz: "Hello World".to_string(),
2218 /// addr: Ipv4Addr::new(127, 0, 0, 1),
2219 /// })
2220 /// );
2221 /// ```
2222 #[stable(feature = "debug_builders", since = "1.2.0")]
2223 pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
2224 builders::debug_struct_new(self, name)
2225 }
2226
2227 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2228 /// binaries. `debug_struct_fields_finish` is more general, but this is
2229 /// faster for 1 field.
2230 #[doc(hidden)]
2231 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2232 pub fn debug_struct_field1_finish<'b>(
2233 &'b mut self,
2234 name: &str,
2235 name1: &str,
2236 value1: &dyn Debug,
2237 ) -> Result {
2238 let mut builder = builders::debug_struct_new(self, name);
2239 builder.field(name1, value1);
2240 builder.finish()
2241 }
2242
2243 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2244 /// binaries. `debug_struct_fields_finish` is more general, but this is
2245 /// faster for 2 fields.
2246 #[doc(hidden)]
2247 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2248 pub fn debug_struct_field2_finish<'b>(
2249 &'b mut self,
2250 name: &str,
2251 name1: &str,
2252 value1: &dyn Debug,
2253 name2: &str,
2254 value2: &dyn Debug,
2255 ) -> Result {
2256 let mut builder = builders::debug_struct_new(self, name);
2257 builder.field(name1, value1);
2258 builder.field(name2, value2);
2259 builder.finish()
2260 }
2261
2262 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2263 /// binaries. `debug_struct_fields_finish` is more general, but this is
2264 /// faster for 3 fields.
2265 #[doc(hidden)]
2266 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2267 pub fn debug_struct_field3_finish<'b>(
2268 &'b mut self,
2269 name: &str,
2270 name1: &str,
2271 value1: &dyn Debug,
2272 name2: &str,
2273 value2: &dyn Debug,
2274 name3: &str,
2275 value3: &dyn Debug,
2276 ) -> Result {
2277 let mut builder = builders::debug_struct_new(self, name);
2278 builder.field(name1, value1);
2279 builder.field(name2, value2);
2280 builder.field(name3, value3);
2281 builder.finish()
2282 }
2283
2284 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2285 /// binaries. `debug_struct_fields_finish` is more general, but this is
2286 /// faster for 4 fields.
2287 #[doc(hidden)]
2288 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2289 pub fn debug_struct_field4_finish<'b>(
2290 &'b mut self,
2291 name: &str,
2292 name1: &str,
2293 value1: &dyn Debug,
2294 name2: &str,
2295 value2: &dyn Debug,
2296 name3: &str,
2297 value3: &dyn Debug,
2298 name4: &str,
2299 value4: &dyn Debug,
2300 ) -> Result {
2301 let mut builder = builders::debug_struct_new(self, name);
2302 builder.field(name1, value1);
2303 builder.field(name2, value2);
2304 builder.field(name3, value3);
2305 builder.field(name4, value4);
2306 builder.finish()
2307 }
2308
2309 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2310 /// binaries. `debug_struct_fields_finish` is more general, but this is
2311 /// faster for 5 fields.
2312 #[doc(hidden)]
2313 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2314 pub fn debug_struct_field5_finish<'b>(
2315 &'b mut self,
2316 name: &str,
2317 name1: &str,
2318 value1: &dyn Debug,
2319 name2: &str,
2320 value2: &dyn Debug,
2321 name3: &str,
2322 value3: &dyn Debug,
2323 name4: &str,
2324 value4: &dyn Debug,
2325 name5: &str,
2326 value5: &dyn Debug,
2327 ) -> Result {
2328 let mut builder = builders::debug_struct_new(self, name);
2329 builder.field(name1, value1);
2330 builder.field(name2, value2);
2331 builder.field(name3, value3);
2332 builder.field(name4, value4);
2333 builder.field(name5, value5);
2334 builder.finish()
2335 }
2336
2337 /// Shrinks `derive(Debug)` code, for faster compilation and smaller binaries.
2338 /// For the cases not covered by `debug_struct_field[12345]_finish`.
2339 #[doc(hidden)]
2340 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2341 pub fn debug_struct_fields_finish<'b>(
2342 &'b mut self,
2343 name: &str,
2344 names: &[&str],
2345 values: &[&dyn Debug],
2346 ) -> Result {
2347 assert_eq!(names.len(), values.len());
2348 let mut builder = builders::debug_struct_new(self, name);
2349 for (name, value) in iter::zip(names, values) {
2350 builder.field(name, value);
2351 }
2352 builder.finish()
2353 }
2354
2355 /// Creates a `DebugTuple` builder designed to assist with creation of
2356 /// `fmt::Debug` implementations for tuple structs.
2357 ///
2358 /// # Examples
2359 ///
2360 /// ```rust
2361 /// use std::fmt;
2362 /// use std::marker::PhantomData;
2363 ///
2364 /// struct Foo<T>(i32, String, PhantomData<T>);
2365 ///
2366 /// impl<T> fmt::Debug for Foo<T> {
2367 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2368 /// fmt.debug_tuple("Foo")
2369 /// .field(&self.0)
2370 /// .field(&self.1)
2371 /// .field(&format_args!("_"))
2372 /// .finish()
2373 /// }
2374 /// }
2375 ///
2376 /// assert_eq!(
2377 /// "Foo(10, \"Hello\", _)",
2378 /// format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
2379 /// );
2380 /// ```
2381 #[stable(feature = "debug_builders", since = "1.2.0")]
2382 pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
2383 builders::debug_tuple_new(self, name)
2384 }
2385
2386 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2387 /// binaries. `debug_tuple_fields_finish` is more general, but this is faster
2388 /// for 1 field.
2389 #[doc(hidden)]
2390 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2391 pub fn debug_tuple_field1_finish<'b>(&'b mut self, name: &str, value1: &dyn Debug) -> Result {
2392 let mut builder = builders::debug_tuple_new(self, name);
2393 builder.field(value1);
2394 builder.finish()
2395 }
2396
2397 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2398 /// binaries. `debug_tuple_fields_finish` is more general, but this is faster
2399 /// for 2 fields.
2400 #[doc(hidden)]
2401 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2402 pub fn debug_tuple_field2_finish<'b>(
2403 &'b mut self,
2404 name: &str,
2405 value1: &dyn Debug,
2406 value2: &dyn Debug,
2407 ) -> Result {
2408 let mut builder = builders::debug_tuple_new(self, name);
2409 builder.field(value1);
2410 builder.field(value2);
2411 builder.finish()
2412 }
2413
2414 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2415 /// binaries. `debug_tuple_fields_finish` is more general, but this is faster
2416 /// for 3 fields.
2417 #[doc(hidden)]
2418 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2419 pub fn debug_tuple_field3_finish<'b>(
2420 &'b mut self,
2421 name: &str,
2422 value1: &dyn Debug,
2423 value2: &dyn Debug,
2424 value3: &dyn Debug,
2425 ) -> Result {
2426 let mut builder = builders::debug_tuple_new(self, name);
2427 builder.field(value1);
2428 builder.field(value2);
2429 builder.field(value3);
2430 builder.finish()
2431 }
2432
2433 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2434 /// binaries. `debug_tuple_fields_finish` is more general, but this is faster
2435 /// for 4 fields.
2436 #[doc(hidden)]
2437 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2438 pub fn debug_tuple_field4_finish<'b>(
2439 &'b mut self,
2440 name: &str,
2441 value1: &dyn Debug,
2442 value2: &dyn Debug,
2443 value3: &dyn Debug,
2444 value4: &dyn Debug,
2445 ) -> Result {
2446 let mut builder = builders::debug_tuple_new(self, name);
2447 builder.field(value1);
2448 builder.field(value2);
2449 builder.field(value3);
2450 builder.field(value4);
2451 builder.finish()
2452 }
2453
2454 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2455 /// binaries. `debug_tuple_fields_finish` is more general, but this is faster
2456 /// for 5 fields.
2457 #[doc(hidden)]
2458 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2459 pub fn debug_tuple_field5_finish<'b>(
2460 &'b mut self,
2461 name: &str,
2462 value1: &dyn Debug,
2463 value2: &dyn Debug,
2464 value3: &dyn Debug,
2465 value4: &dyn Debug,
2466 value5: &dyn Debug,
2467 ) -> Result {
2468 let mut builder = builders::debug_tuple_new(self, name);
2469 builder.field(value1);
2470 builder.field(value2);
2471 builder.field(value3);
2472 builder.field(value4);
2473 builder.field(value5);
2474 builder.finish()
2475 }
2476
2477 /// Shrinks `derive(Debug)` code, for faster compilation and smaller
2478 /// binaries. For the cases not covered by `debug_tuple_field[12345]_finish`.
2479 #[doc(hidden)]
2480 #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
2481 pub fn debug_tuple_fields_finish<'b>(
2482 &'b mut self,
2483 name: &str,
2484 values: &[&dyn Debug],
2485 ) -> Result {
2486 let mut builder = builders::debug_tuple_new(self, name);
2487 for value in values {
2488 builder.field(value);
2489 }
2490 builder.finish()
2491 }
2492
2493 /// Creates a `DebugList` builder designed to assist with creation of
2494 /// `fmt::Debug` implementations for list-like structures.
2495 ///
2496 /// # Examples
2497 ///
2498 /// ```rust
2499 /// use std::fmt;
2500 ///
2501 /// struct Foo(Vec<i32>);
2502 ///
2503 /// impl fmt::Debug for Foo {
2504 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2505 /// fmt.debug_list().entries(self.0.iter()).finish()
2506 /// }
2507 /// }
2508 ///
2509 /// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]");
2510 /// ```
2511 #[stable(feature = "debug_builders", since = "1.2.0")]
2512 pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
2513 builders::debug_list_new(self)
2514 }
2515
2516 /// Creates a `DebugSet` builder designed to assist with creation of
2517 /// `fmt::Debug` implementations for set-like structures.
2518 ///
2519 /// # Examples
2520 ///
2521 /// ```rust
2522 /// use std::fmt;
2523 ///
2524 /// struct Foo(Vec<i32>);
2525 ///
2526 /// impl fmt::Debug for Foo {
2527 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2528 /// fmt.debug_set().entries(self.0.iter()).finish()
2529 /// }
2530 /// }
2531 ///
2532 /// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "{10, 11}");
2533 /// ```
2534 ///
2535 /// [`format_args!`]: crate::format_args
2536 ///
2537 /// In this more complex example, we use [`format_args!`] and `.debug_set()`
2538 /// to build a list of match arms:
2539 ///
2540 /// ```rust
2541 /// use std::fmt;
2542 ///
2543 /// struct Arm<'a, L, R>(&'a (L, R));
2544 /// struct Table<'a, K, V>(&'a [(K, V)], V);
2545 ///
2546 /// impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
2547 /// where
2548 /// L: 'a + fmt::Debug, R: 'a + fmt::Debug
2549 /// {
2550 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2551 /// L::fmt(&(self.0).0, fmt)?;
2552 /// fmt.write_str(" => ")?;
2553 /// R::fmt(&(self.0).1, fmt)
2554 /// }
2555 /// }
2556 ///
2557 /// impl<'a, K, V> fmt::Debug for Table<'a, K, V>
2558 /// where
2559 /// K: 'a + fmt::Debug, V: 'a + fmt::Debug
2560 /// {
2561 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2562 /// fmt.debug_set()
2563 /// .entries(self.0.iter().map(Arm))
2564 /// .entry(&Arm(&(format_args!("_"), &self.1)))
2565 /// .finish()
2566 /// }
2567 /// }
2568 /// ```
2569 #[stable(feature = "debug_builders", since = "1.2.0")]
2570 pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
2571 builders::debug_set_new(self)
2572 }
2573
2574 /// Creates a `DebugMap` builder designed to assist with creation of
2575 /// `fmt::Debug` implementations for map-like structures.
2576 ///
2577 /// # Examples
2578 ///
2579 /// ```rust
2580 /// use std::fmt;
2581 ///
2582 /// struct Foo(Vec<(String, i32)>);
2583 ///
2584 /// impl fmt::Debug for Foo {
2585 /// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
2586 /// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
2587 /// }
2588 /// }
2589 ///
2590 /// assert_eq!(
2591 /// format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
2592 /// r#"{"A": 10, "B": 11}"#
2593 /// );
2594 /// ```
2595 #[stable(feature = "debug_builders", since = "1.2.0")]
2596 pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
2597 builders::debug_map_new(self)
2598 }
2599
2600 /// Returns the sign of this formatter (`+` or `-`).
2601 #[unstable(feature = "formatting_options", issue = "118117")]
2602 pub const fn sign(&self) -> Option<Sign> {
2603 self.options.get_sign()
2604 }
2605
2606 /// Returns the formatting options this formatter corresponds to.
2607 #[unstable(feature = "formatting_options", issue = "118117")]
2608 pub const fn options(&self) -> FormattingOptions {
2609 self.options
2610 }
2611}
2612
2613#[stable(since = "1.2.0", feature = "formatter_write")]
2614impl Write for Formatter<'_> {
2615 fn write_str(&mut self, s: &str) -> Result {
2616 self.buf.write_str(s)
2617 }
2618
2619 fn write_char(&mut self, c: char) -> Result {
2620 self.buf.write_char(c)
2621 }
2622
2623 #[inline]
2624 fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
2625 if let Some(s) = args.as_statically_known_str() {
2626 self.buf.write_str(s)
2627 } else {
2628 write(self.buf, args)
2629 }
2630 }
2631}
2632
2633#[stable(feature = "rust1", since = "1.0.0")]
2634impl Display for Error {
2635 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2636 Display::fmt("an error occurred when formatting an argument", f)
2637 }
2638}
2639
2640// Implementations of the core formatting traits
2641
2642macro_rules! fmt_refs {
2643 ($($tr:ident),*) => {
2644 $(
2645 #[stable(feature = "rust1", since = "1.0.0")]
2646 impl<T: ?Sized + $tr> $tr for &T {
2647 fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
2648 }
2649 #[stable(feature = "rust1", since = "1.0.0")]
2650 impl<T: ?Sized + $tr> $tr for &mut T {
2651 fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
2652 }
2653 )*
2654 }
2655}
2656
2657fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
2658
2659#[unstable(feature = "never_type", issue = "35121")]
2660impl Debug for ! {
2661 #[inline]
2662 fn fmt(&self, _: &mut Formatter<'_>) -> Result {
2663 *self
2664 }
2665}
2666
2667#[unstable(feature = "never_type", issue = "35121")]
2668impl Display for ! {
2669 #[inline]
2670 fn fmt(&self, _: &mut Formatter<'_>) -> Result {
2671 *self
2672 }
2673}
2674
2675#[stable(feature = "rust1", since = "1.0.0")]
2676impl Debug for bool {
2677 #[inline]
2678 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2679 Display::fmt(self, f)
2680 }
2681}
2682
2683#[stable(feature = "rust1", since = "1.0.0")]
2684impl Display for bool {
2685 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2686 Display::fmt(if *self { "true" } else { "false" }, f)
2687 }
2688}
2689
2690#[stable(feature = "rust1", since = "1.0.0")]
2691impl Debug for str {
2692 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2693 f.write_char('"')?;
2694
2695 // substring we know is printable
2696 let mut printable_range = 0..0;
2697
2698 fn needs_escape(b: u8) -> bool {
2699 b > 0x7E || b < 0x20 || b == b'\\' || b == b'"'
2700 }
2701
2702 // the loop here first skips over runs of printable ASCII as a fast path.
2703 // other chars (unicode, or ASCII that needs escaping) are then handled per-`char`.
2704 let mut rest = self;
2705 while rest.len() > 0 {
2706 let Some(non_printable_start) = rest.as_bytes().iter().position(|&b| needs_escape(b))
2707 else {
2708 printable_range.end += rest.len();
2709 break;
2710 };
2711
2712 printable_range.end += non_printable_start;
2713 // SAFETY: the position was derived from an iterator, so is known to be within bounds, and at a char boundary
2714 rest = unsafe { rest.get_unchecked(non_printable_start..) };
2715
2716 let mut chars = rest.chars();
2717 if let Some(c) = chars.next() {
2718 let esc = c.escape_debug_ext(EscapeDebugExtArgs {
2719 escape_grapheme_extended: true,
2720 escape_single_quote: false,
2721 escape_double_quote: true,
2722 });
2723 if esc.len() != 1 {
2724 f.write_str(&self[printable_range.clone()])?;
2725 Display::fmt(&esc, f)?;
2726 printable_range.start = printable_range.end + c.len_utf8();
2727 }
2728 printable_range.end += c.len_utf8();
2729 }
2730 rest = chars.as_str();
2731 }
2732
2733 f.write_str(&self[printable_range])?;
2734
2735 f.write_char('"')
2736 }
2737}
2738
2739#[stable(feature = "rust1", since = "1.0.0")]
2740impl Display for str {
2741 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2742 f.pad(self)
2743 }
2744}
2745
2746#[stable(feature = "rust1", since = "1.0.0")]
2747impl Debug for char {
2748 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2749 f.write_char('\'')?;
2750 let esc = self.escape_debug_ext(EscapeDebugExtArgs {
2751 escape_grapheme_extended: true,
2752 escape_single_quote: true,
2753 escape_double_quote: false,
2754 });
2755 Display::fmt(&esc, f)?;
2756 f.write_char('\'')
2757 }
2758}
2759
2760#[stable(feature = "rust1", since = "1.0.0")]
2761impl Display for char {
2762 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2763 if f.options.width.is_none() && f.options.precision.is_none() {
2764 f.write_char(*self)
2765 } else {
2766 f.pad(self.encode_utf8(&mut [0; MAX_LEN_UTF8]))
2767 }
2768 }
2769}
2770
2771#[stable(feature = "rust1", since = "1.0.0")]
2772impl<T: ?Sized> Pointer for *const T {
2773 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2774 pointer_fmt_inner(self.expose_provenance(), f)
2775 }
2776}
2777
2778/// Since the formatting will be identical for all pointer types, uses a
2779/// non-monomorphized implementation for the actual formatting to reduce the
2780/// amount of codegen work needed.
2781///
2782/// This uses `ptr_addr: usize` and not `ptr: *const ()` to be able to use this for
2783/// `fn(...) -> ...` without using [problematic] "Oxford Casts".
2784///
2785/// [problematic]: https://github.com/rust-lang/rust/issues/95489
2786pub(crate) fn pointer_fmt_inner(ptr_addr: usize, f: &mut Formatter<'_>) -> Result {
2787 let old_width = f.options.width;
2788 let old_flags = f.options.flags;
2789
2790 // The alternate flag is already treated by LowerHex as being special-
2791 // it denotes whether to prefix with 0x. We use it to work out whether
2792 // or not to zero extend, and then unconditionally set it to get the
2793 // prefix.
2794 if f.alternate() {
2795 f.options.flags |= 1 << (rt::Flag::SignAwareZeroPad as u32);
2796
2797 if f.options.width.is_none() {
2798 f.options.width = Some((usize::BITS / 4) as u16 + 2);
2799 }
2800 }
2801 f.options.flags |= 1 << (rt::Flag::Alternate as u32);
2802
2803 let ret = LowerHex::fmt(&ptr_addr, f);
2804
2805 f.options.width = old_width;
2806 f.options.flags = old_flags;
2807
2808 ret
2809}
2810
2811#[stable(feature = "rust1", since = "1.0.0")]
2812impl<T: ?Sized> Pointer for *mut T {
2813 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2814 Pointer::fmt(&(*self as *const T), f)
2815 }
2816}
2817
2818#[stable(feature = "rust1", since = "1.0.0")]
2819impl<T: ?Sized> Pointer for &T {
2820 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2821 Pointer::fmt(&(*self as *const T), f)
2822 }
2823}
2824
2825#[stable(feature = "rust1", since = "1.0.0")]
2826impl<T: ?Sized> Pointer for &mut T {
2827 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2828 Pointer::fmt(&(&**self as *const T), f)
2829 }
2830}
2831
2832// Implementation of Display/Debug for various core types
2833
2834#[stable(feature = "rust1", since = "1.0.0")]
2835impl<T: ?Sized> Debug for *const T {
2836 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2837 Pointer::fmt(self, f)
2838 }
2839}
2840#[stable(feature = "rust1", since = "1.0.0")]
2841impl<T: ?Sized> Debug for *mut T {
2842 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2843 Pointer::fmt(self, f)
2844 }
2845}
2846
2847macro_rules! peel {
2848 ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
2849}
2850
2851macro_rules! tuple {
2852 () => ();
2853 ( $($name:ident,)+ ) => (
2854 maybe_tuple_doc! {
2855 $($name)+ @
2856 #[stable(feature = "rust1", since = "1.0.0")]
2857 impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
2858 #[allow(non_snake_case, unused_assignments)]
2859 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2860 let mut builder = f.debug_tuple("");
2861 let ($(ref $name,)+) = *self;
2862 $(
2863 builder.field(&$name);
2864 )+
2865
2866 builder.finish()
2867 }
2868 }
2869 }
2870 peel! { $($name,)+ }
2871 )
2872}
2873
2874macro_rules! maybe_tuple_doc {
2875 ($a:ident @ #[$meta:meta] $item:item) => {
2876 #[doc(fake_variadic)]
2877 #[doc = "This trait is implemented for tuples up to twelve items long."]
2878 #[$meta]
2879 $item
2880 };
2881 ($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
2882 #[doc(hidden)]
2883 #[$meta]
2884 $item
2885 };
2886}
2887
2888macro_rules! last_type {
2889 ($a:ident,) => { $a };
2890 ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
2891}
2892
2893tuple! { E, D, C, B, A, Z, Y, X, W, V, U, T, }
2894
2895#[stable(feature = "rust1", since = "1.0.0")]
2896impl<T: Debug> Debug for [T] {
2897 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2898 f.debug_list().entries(self.iter()).finish()
2899 }
2900}
2901
2902#[stable(feature = "rust1", since = "1.0.0")]
2903impl Debug for () {
2904 #[inline]
2905 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2906 f.pad("()")
2907 }
2908}
2909#[stable(feature = "rust1", since = "1.0.0")]
2910impl<T: ?Sized> Debug for PhantomData<T> {
2911 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2912 write!(f, "PhantomData<{}>", crate::any::type_name::<T>())
2913 }
2914}
2915
2916#[stable(feature = "rust1", since = "1.0.0")]
2917impl<T: Copy + Debug> Debug for Cell<T> {
2918 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2919 f.debug_struct("Cell").field("value", &self.get()).finish()
2920 }
2921}
2922
2923#[stable(feature = "rust1", since = "1.0.0")]
2924impl<T: ?Sized + Debug> Debug for RefCell<T> {
2925 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2926 let mut d = f.debug_struct("RefCell");
2927 match self.try_borrow() {
2928 Ok(borrow) => d.field("value", &borrow),
2929 Err(_) => d.field("value", &format_args!("<borrowed>")),
2930 };
2931 d.finish()
2932 }
2933}
2934
2935#[stable(feature = "rust1", since = "1.0.0")]
2936impl<T: ?Sized + Debug> Debug for Ref<'_, T> {
2937 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2938 Debug::fmt(&**self, f)
2939 }
2940}
2941
2942#[stable(feature = "rust1", since = "1.0.0")]
2943impl<T: ?Sized + Debug> Debug for RefMut<'_, T> {
2944 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2945 Debug::fmt(&*(self.deref()), f)
2946 }
2947}
2948
2949#[stable(feature = "core_impl_debug", since = "1.9.0")]
2950impl<T: ?Sized> Debug for UnsafeCell<T> {
2951 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2952 f.debug_struct("UnsafeCell").finish_non_exhaustive()
2953 }
2954}
2955
2956#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
2957impl<T: ?Sized> Debug for SyncUnsafeCell<T> {
2958 fn fmt(&self, f: &mut Formatter<'_>) -> Result {
2959 f.debug_struct("SyncUnsafeCell").finish_non_exhaustive()
2960 }
2961}
2962
2963// If you expected tests to be here, look instead at the core/tests/fmt.rs file,
2964// it's a lot easier than creating all of the rt::Piece structures here.
2965// There are also tests in the alloc crate, for those that need allocations.