1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
//! Utilities for formatting and printing `String`s.
//!
//! This module contains the runtime support for the [`format!`] syntax extension.
//! This macro is implemented in the compiler to emit calls to this module in
//! order to format arguments at runtime into strings.
//!
//! # Usage
//!
//! The [`format!`] macro is intended to be familiar to those coming from C's
//! `printf`/`fprintf` functions or Python's `str.format` function.
//!
//! Some examples of the [`format!`] extension are:
//!
//! ```
//! format!("Hello");                 // => "Hello"
//! format!("Hello, {}!", "world");   // => "Hello, world!"
//! format!("The number is {}", 1);   // => "The number is 1"
//! format!("{:?}", (3, 4));          // => "(3, 4)"
//! format!("{value}", value=4);      // => "4"
//! let people = "Rustaceans";
//! format!("Hello {people}!");       // => "Hello Rustaceans!"
//! format!("{} {}", 1, 2);           // => "1 2"
//! format!("{:04}", 42);             // => "0042" with leading zeros
//! format!("{:#?}", (100, 200));     // => "(
//!                                   //       100,
//!                                   //       200,
//!                                   //     )"
//! ```
//!
//! From these, you can see that the first argument is a format string. It is
//! required by the compiler for this to be a string literal; it cannot be a
//! variable passed in (in order to perform validity checking). The compiler
//! will then parse the format string and determine if the list of arguments
//! provided is suitable to pass to this format string.
//!
//! To convert a single value to a string, use the [`to_string`] method. This
//! will use the [`Display`] formatting trait.
//!
//! ## Positional parameters
//!
//! Each formatting argument is allowed to specify which value argument it's
//! referencing, and if omitted it is assumed to be "the next argument". For
//! example, the format string `{} {} {}` would take three parameters, and they
//! would be formatted in the same order as they're given. The format string
//! `{2} {1} {0}`, however, would format arguments in reverse order.
//!
//! Things can get a little tricky once you start intermingling the two types of
//! positional specifiers. The "next argument" specifier can be thought of as an
//! iterator over the argument. Each time a "next argument" specifier is seen,
//! the iterator advances. This leads to behavior like this:
//!
//! ```
//! format!("{1} {} {0} {}", 1, 2); // => "2 1 1 2"
//! ```
//!
//! The internal iterator over the argument has not been advanced by the time
//! the first `{}` is seen, so it prints the first argument. Then upon reaching
//! the second `{}`, the iterator has advanced forward to the second argument.
//! Essentially, parameters that explicitly name their argument do not affect
//! parameters that do not name an argument in terms of positional specifiers.
//!
//! A format string is required to use all of its arguments, otherwise it is a
//! compile-time error. You may refer to the same argument more than once in the
//! format string.
//!
//! ## Named parameters
//!
//! Rust itself does not have a Python-like equivalent of named parameters to a
//! function, but the [`format!`] macro is a syntax extension that allows it to
//! leverage named parameters. Named parameters are listed at the end of the
//! argument list and have the syntax:
//!
//! ```text
//! identifier '=' expression
//! ```
//!
//! For example, the following [`format!`] expressions all use named arguments:
//!
//! ```
//! format!("{argument}", argument = "test");   // => "test"
//! format!("{name} {}", 1, name = 2);          // => "2 1"
//! format!("{a} {c} {b}", a="a", b='b', c=3);  // => "a 3 b"
//! ```
//!
//! If a named parameter does not appear in the argument list, `format!` will
//! reference a variable with that name in the current scope.
//!
//! ```
//! let argument = 2 + 2;
//! format!("{argument}");   // => "4"
//!
//! fn make_string(a: u32, b: &str) -> String {
//!     format!("{b} {a}")
//! }
//! make_string(927, "label"); // => "label 927"
//! ```
//!
//! It is not valid to put positional parameters (those without names) after
//! arguments that have names. Like with positional parameters, it is not
//! valid to provide named parameters that are unused by the format string.
//!
//! # Formatting Parameters
//!
//! Each argument being formatted can be transformed by a number of formatting
//! parameters (corresponding to `format_spec` in [the syntax](#syntax)). These
//! parameters affect the string representation of what's being formatted.
//!
//! ## Width
//!
//! ```
//! // All of these print "Hello x    !"
//! println!("Hello {:5}!", "x");
//! println!("Hello {:1$}!", "x", 5);
//! println!("Hello {1:0$}!", 5, "x");
//! println!("Hello {:width$}!", "x", width = 5);
//! let width = 5;
//! println!("Hello {:width$}!", "x");
//! ```
//!
//! This is a parameter for the "minimum width" that the format should take up.
//! If the value's string does not fill up this many characters, then the
//! padding specified by fill/alignment will be used to take up the required
//! space (see below).
//!
//! The value for the width can also be provided as a [`usize`] in the list of
//! parameters by adding a postfix `$`, indicating that the second argument is
//! a [`usize`] specifying the width.
//!
//! Referring to an argument with the dollar syntax does not affect the "next
//! argument" counter, so it's usually a good idea to refer to arguments by
//! position, or use named arguments.
//!
//! ## Fill/Alignment
//!
//! ```
//! assert_eq!(format!("Hello {:<5}!", "x"),  "Hello x    !");
//! assert_eq!(format!("Hello {:-<5}!", "x"), "Hello x----!");
//! assert_eq!(format!("Hello {:^5}!", "x"),  "Hello   x  !");
//! assert_eq!(format!("Hello {:>5}!", "x"),  "Hello     x!");
//! ```
//!
//! The optional fill character and alignment is provided normally in conjunction with the
//! [`width`](#width) parameter. It must be defined before `width`, right after the `:`.
//! This indicates that if the value being formatted is smaller than
//! `width` some extra characters will be printed around it.
//! Filling comes in the following variants for different alignments:
//!
//! * `[fill]<` - the argument is left-aligned in `width` columns
//! * `[fill]^` - the argument is center-aligned in `width` columns
//! * `[fill]>` - the argument is right-aligned in `width` columns
//!
//! The default [fill/alignment](#fillalignment) for non-numerics is a space and
//! left-aligned. The
//! default for numeric formatters is also a space character but with right-alignment. If
//! the `0` flag (see below) is specified for numerics, then the implicit fill character is
//! `0`.
//!
//! Note that alignment might not be implemented by some types. In particular, it
//! is not generally implemented for the `Debug` trait.  A good way to ensure
//! padding is applied is to format your input, then pad this resulting string
//! to obtain your output:
//!
//! ```
//! println!("Hello {:^15}!", format!("{:?}", Some("hi"))); // => "Hello   Some("hi")   !"
//! ```
//!
//! ## Sign/`#`/`0`
//!
//! ```
//! assert_eq!(format!("Hello {:+}!", 5), "Hello +5!");
//! assert_eq!(format!("{:#x}!", 27), "0x1b!");
//! assert_eq!(format!("Hello {:05}!", 5),  "Hello 00005!");
//! assert_eq!(format!("Hello {:05}!", -5), "Hello -0005!");
//! assert_eq!(format!("{:#010x}!", 27), "0x0000001b!");
//! ```
//!
//! These are all flags altering the behavior of the formatter.
//!
//! * `+` - This is intended for numeric types and indicates that the sign
//!         should always be printed. By default only the negative sign of signed values
//!         is printed, and the sign of positive or unsigned values is omitted.
//!         This flag indicates that the correct sign (`+` or `-`) should always be printed.
//! * `-` - Currently not used
//! * `#` - This flag indicates that the "alternate" form of printing should
//!         be used. The alternate forms are:
//!     * `#?` - pretty-print the [`Debug`] formatting (adds linebreaks and indentation)
//!     * `#x` - precedes the argument with a `0x`
//!     * `#X` - precedes the argument with a `0x`
//!     * `#b` - precedes the argument with a `0b`
//!     * `#o` - precedes the argument with a `0o`
//! * `0` - 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. A format
//!         like `{:08}` would yield `00000001` for the integer `1`, while the
//!         same format would yield `-0000001` for the integer `-1`. Notice that
//!         the negative version has one fewer zero than the positive version.
//!         Note that padding zeros are always placed after the sign (if any)
//!         and before the digits. When used together with the `#` flag, a similar
//!         rule applies: padding zeros are inserted after the prefix but before
//!         the digits. The prefix is included in the total width.
//!
//! ## Precision
//!
//! For non-numeric types, this can be considered a "maximum width". If the resulting string is
//! longer than this width, then it is truncated down to this many characters and that truncated
//! value is emitted with proper `fill`, `alignment` and `width` if those parameters are set.
//!
//! For integral types, this is ignored.
//!
//! For floating-point types, this indicates how many digits after the decimal point should be
//! printed.
//!
//! There are three possible ways to specify the desired `precision`:
//!
//! 1. An integer `.N`:
//!
//!    the integer `N` itself is the precision.
//!
//! 2. An integer or name followed by dollar sign `.N$`:
//!
//!    use format *argument* `N` (which must be a `usize`) as the precision.
//!
//! 3. An asterisk `.*`:
//!
//!    `.*` means that this `{...}` is associated with *two* format inputs rather than one:
//!    - If a format string in the fashion of `{:<spec>.*}` is used, then the first input holds
//!      the `usize` precision, and the second holds the value to print.
//!    - If a format string in the fashion of `{<arg>:<spec>.*}` is used, then the `<arg>` part
//!      refers to the value to print, and the `precision` is taken like it was specified with an
//!      omitted positional parameter (`{}` instead of `{<arg>:}`).
//!
//! For example, the following calls all print the same thing `Hello x is 0.01000`:
//!
//! ```
//! // Hello {arg 0 ("x")} is {arg 1 (0.01) with precision specified inline (5)}
//! println!("Hello {0} is {1:.5}", "x", 0.01);
//!
//! // Hello {arg 1 ("x")} is {arg 2 (0.01) with precision specified in arg 0 (5)}
//! println!("Hello {1} is {2:.0$}", 5, "x", 0.01);
//!
//! // Hello {arg 0 ("x")} is {arg 2 (0.01) with precision specified in arg 1 (5)}
//! println!("Hello {0} is {2:.1$}", "x", 5, 0.01);
//!
//! // Hello {next arg -> arg 0 ("x")} is {second of next two args -> arg 2 (0.01) with precision
//! //                          specified in first of next two args -> arg 1 (5)}
//! println!("Hello {} is {:.*}",    "x", 5, 0.01);
//!
//! // Hello {arg 1 ("x")} is {arg 2 (0.01) with precision
//! //                          specified in next arg -> arg 0 (5)}
//! println!("Hello {1} is {2:.*}",  5, "x", 0.01);
//!
//! // Hello {next arg -> arg 0 ("x")} is {arg 2 (0.01) with precision
//! //                          specified in next arg -> arg 1 (5)}
//! println!("Hello {} is {2:.*}",   "x", 5, 0.01);
//!
//! // Hello {next arg -> arg 0 ("x")} is {arg "number" (0.01) with precision specified
//! //                          in arg "prec" (5)}
//! println!("Hello {} is {number:.prec$}", "x", prec = 5, number = 0.01);
//! ```
//!
//! While these:
//!
//! ```
//! println!("{}, `{name:.*}` has 3 fractional digits", "Hello", 3, name=1234.56);
//! println!("{}, `{name:.*}` has 3 characters", "Hello", 3, name="1234.56");
//! println!("{}, `{name:>8.*}` has 3 right-aligned characters", "Hello", 3, name="1234.56");
//! ```
//!
//! print three significantly different things:
//!
//! ```text
//! Hello, `1234.560` has 3 fractional digits
//! Hello, `123` has 3 characters
//! Hello, `     123` has 3 right-aligned characters
//! ```
//!
//! ## Localization
//!
//! In some programming languages, the behavior of string formatting functions
//! depends on the operating system's locale setting. The format functions
//! provided by Rust's standard library do not have any concept of locale and
//! will produce the same results on all systems regardless of user
//! configuration.
//!
//! For example, the following code will always print `1.5` even if the system
//! locale uses a decimal separator other than a dot.
//!
//! ```
//! println!("The value is {}", 1.5);
//! ```
//!
//! # Escaping
//!
//! The literal characters `{` and `}` may be included in a string by preceding
//! them with the same character. For example, the `{` character is escaped with
//! `{{` and the `}` character is escaped with `}}`.
//!
//! ```
//! assert_eq!(format!("Hello {{}}"), "Hello {}");
//! assert_eq!(format!("{{ Hello"), "{ Hello");
//! ```
//!
//! # Syntax
//!
//! To summarize, here you can find the full grammar of format strings.
//! The syntax for the formatting language used is drawn from other languages,
//! so it should not be too alien. Arguments are formatted with Python-like
//! syntax, meaning that arguments are surrounded by `{}` instead of the C-like
//! `%`. The actual grammar for the formatting syntax is:
//!
//! ```text
//! format_string := text [ maybe_format text ] *
//! maybe_format := '{' '{' | '}' '}' | format
//! format := '{' [ argument ] [ ':' format_spec ] [ ws ] * '}'
//! argument := integer | identifier
//!
//! format_spec := [[fill]align][sign]['#']['0'][width]['.' precision]type
//! fill := character
//! align := '<' | '^' | '>'
//! sign := '+' | '-'
//! width := count
//! precision := count | '*'
//! type := '' | '?' | 'x?' | 'X?' | identifier
//! count := parameter | integer
//! parameter := argument '$'
//! ```
//! In the above grammar,
//! - `text` must not contain any `'{'` or `'}'` characters,
//! - `ws` is any character for which [`char::is_whitespace`] returns `true`, has no semantic
//!   meaning and is completely optional,
//! - `integer` is a decimal integer that may contain leading zeroes and must fit into an `usize` and
//! - `identifier` is an `IDENTIFIER_OR_KEYWORD` (not an `IDENTIFIER`) as defined by the [Rust language reference](https://doc.rust-lang.org/reference/identifiers.html).
//!
//! # Formatting traits
//!
//! When requesting that an argument be formatted with a particular type, you
//! are actually requesting that an argument ascribes to a particular trait.
//! This allows multiple actual types to be formatted via `{:x}` (like [`i8`] as
//! well as [`isize`]). The current mapping of types to traits is:
//!
//! * *nothing* ⇒ [`Display`]
//! * `?` ⇒ [`Debug`]
//! * `x?` ⇒ [`Debug`] with lower-case hexadecimal integers
//! * `X?` ⇒ [`Debug`] with upper-case hexadecimal integers
//! * `o` ⇒ [`Octal`]
//! * `x` ⇒ [`LowerHex`]
//! * `X` ⇒ [`UpperHex`]
//! * `p` ⇒ [`Pointer`]
//! * `b` ⇒ [`Binary`]
//! * `e` ⇒ [`LowerExp`]
//! * `E` ⇒ [`UpperExp`]
//!
//! What this means is that any type of argument which implements the
//! [`fmt::Binary`][`Binary`] trait can then be formatted with `{:b}`. Implementations
//! are provided for these traits for a number of primitive types by the
//! standard library as well. If no format is specified (as in `{}` or `{:6}`),
//! then the format trait used is the [`Display`] trait.
//!
//! When implementing a format trait for your own type, you will have to
//! implement a method of the signature:
//!
//! ```
//! # #![allow(dead_code)]
//! # use std::fmt;
//! # struct Foo; // our custom type
//! # impl fmt::Display for Foo {
//! fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
//! # write!(f, "testing, testing")
//! # } }
//! ```
//!
//! Your type will be passed as `self` by-reference, and then the function
//! should emit output into the Formatter `f` which implements `fmt::Write`. It is up to each
//! format trait implementation to correctly adhere to the requested formatting parameters.
//! The values of these parameters can be accessed with methods of the
//! [`Formatter`] struct. In order to help with this, the [`Formatter`] struct also
//! provides some helper methods.
//!
//! Additionally, the return value of this function is [`fmt::Result`] which is a
//! type alias of <code>[Result]<(), [std::fmt::Error]></code>. Formatting implementations
//! should ensure that they propagate errors from the [`Formatter`] (e.g., when
//! calling [`write!`]). However, they should never return errors spuriously. That
//! is, a formatting implementation must and may only return an error if the
//! passed-in [`Formatter`] returns an error. This is because, contrary to what
//! the function signature might suggest, string formatting is an infallible
//! operation. This function only returns a result because writing to the
//! underlying stream might fail and it must provide a way to propagate the fact
//! that an error has occurred back up the stack.
//!
//! An example of implementing the formatting traits would look
//! like:
//!
//! ```
//! use std::fmt;
//!
//! #[derive(Debug)]
//! struct Vector2D {
//!     x: isize,
//!     y: isize,
//! }
//!
//! impl fmt::Display for Vector2D {
//!     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
//!         // The `f` value implements the `Write` trait, which is what the
//!         // write! macro is expecting. Note that this formatting ignores the
//!         // various flags provided to format strings.
//!         write!(f, "({}, {})", self.x, self.y)
//!     }
//! }
//!
//! // Different traits allow different forms of output of a type. The meaning
//! // of this format is to print the magnitude of a vector.
//! impl fmt::Binary for Vector2D {
//!     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
//!         let magnitude = (self.x * self.x + self.y * self.y) as f64;
//!         let magnitude = magnitude.sqrt();
//!
//!         // Respect the formatting flags by using the helper method
//!         // `pad_integral` on the Formatter object. See the method
//!         // documentation for details, and the function `pad` can be used
//!         // to pad strings.
//!         let decimals = f.precision().unwrap_or(3);
//!         let string = format!("{magnitude:.decimals$}");
//!         f.pad_integral(true, "", &string)
//!     }
//! }
//!
//! fn main() {
//!     let myvector = Vector2D { x: 3, y: 4 };
//!
//!     println!("{myvector}");       // => "(3, 4)"
//!     println!("{myvector:?}");     // => "Vector2D {x: 3, y:4}"
//!     println!("{myvector:10.3b}"); // => "     5.000"
//! }
//! ```
//!
//! ### `fmt::Display` vs `fmt::Debug`
//!
//! These two formatting traits have distinct purposes:
//!
//! - [`fmt::Display`][`Display`] implementations assert that the type can be faithfully
//!   represented as a UTF-8 string at all times. It is **not** expected that
//!   all types implement the [`Display`] trait.
//! - [`fmt::Debug`][`Debug`] implementations should be implemented for **all** public types.
//!   Output will typically represent the internal state as faithfully as possible.
//!   The purpose of the [`Debug`] trait is to facilitate debugging Rust code. In
//!   most cases, using `#[derive(Debug)]` is sufficient and recommended.
//!
//! Some examples of the output from both traits:
//!
//! ```
//! assert_eq!(format!("{} {:?}", 3, 4), "3 4");
//! assert_eq!(format!("{} {:?}", 'a', 'b'), "a 'b'");
//! assert_eq!(format!("{} {:?}", "foo\n", "bar\n"), "foo\n \"bar\\n\"");
//! ```
//!
//! # Related macros
//!
//! There are a number of related macros in the [`format!`] family. The ones that
//! are currently implemented are:
//!
//! ```ignore (only-for-syntax-highlight)
//! format!      // described above
//! write!       // first argument is either a &mut io::Write or a &mut fmt::Write, the destination
//! writeln!     // same as write but appends a newline
//! print!       // the format string is printed to the standard output
//! println!     // same as print but appends a newline
//! eprint!      // the format string is printed to the standard error
//! eprintln!    // same as eprint but appends a newline
//! format_args! // described below.
//! ```
//!
//! ### `write!`
//!
//! [`write!`] and [`writeln!`] are two macros which are used to emit the format string
//! to a specified stream. This is used to prevent intermediate allocations of
//! format strings and instead directly write the output. Under the hood, this
//! function is actually invoking the [`write_fmt`] function defined on the
//! [`std::io::Write`] and the [`std::fmt::Write`] trait. Example usage is:
//!
//! ```
//! # #![allow(unused_must_use)]
//! use std::io::Write;
//! let mut w = Vec::new();
//! write!(&mut w, "Hello {}!", "world");
//! ```
//!
//! ### `print!`
//!
//! This and [`println!`] emit their output to stdout. Similarly to the [`write!`]
//! macro, the goal of these macros is to avoid intermediate allocations when
//! printing output. Example usage is:
//!
//! ```
//! print!("Hello {}!", "world");
//! println!("I have a newline {}", "character at the end");
//! ```
//! ### `eprint!`
//!
//! The [`eprint!`] and [`eprintln!`] macros are identical to
//! [`print!`] and [`println!`], respectively, except they emit their
//! output to stderr.
//!
//! ### `format_args!`
//!
//! [`format_args!`] is a curious macro used to safely pass around
//! an opaque object describing the format string. This object
//! does not require any heap allocations to create, and it only
//! references information on the stack. Under the hood, all of
//! the related macros are implemented in terms of this. First
//! off, some example usage is:
//!
//! ```
//! # #![allow(unused_must_use)]
//! use std::fmt;
//! use std::io::{self, Write};
//!
//! let mut some_writer = io::stdout();
//! write!(&mut some_writer, "{}", format_args!("print with a {}", "macro"));
//!
//! fn my_fmt_fn(args: fmt::Arguments<'_>) {
//!     write!(&mut io::stdout(), "{args}");
//! }
//! my_fmt_fn(format_args!(", or a {} too", "function"));
//! ```
//!
//! The result of the [`format_args!`] macro is a value of type [`fmt::Arguments`].
//! This structure can then be passed to the [`write`] and [`format`] functions
//! inside this module in order to process the format string.
//! The goal of this macro is to even further prevent intermediate allocations
//! when dealing with formatting strings.
//!
//! For example, a logging library could use the standard formatting syntax, but
//! it would internally pass around this structure until it has been determined
//! where output should go to.
//!
//! [`fmt::Result`]: Result "fmt::Result"
//! [Result]: core::result::Result "std::result::Result"
//! [std::fmt::Error]: Error "fmt::Error"
//! [`write`]: write() "fmt::write"
//! [`to_string`]: crate::string::ToString::to_string "ToString::to_string"
//! [`write_fmt`]: ../../std/io/trait.Write.html#method.write_fmt
//! [`std::io::Write`]: ../../std/io/trait.Write.html
//! [`std::fmt::Write`]: ../../std/fmt/trait.Write.html
//! [`print!`]: ../../std/macro.print.html "print!"
//! [`println!`]: ../../std/macro.println.html "println!"
//! [`eprint!`]: ../../std/macro.eprint.html "eprint!"
//! [`eprintln!`]: ../../std/macro.eprintln.html "eprintln!"
//! [`format_args!`]: ../../std/macro.format_args.html "format_args!"
//! [`fmt::Arguments`]: Arguments "fmt::Arguments"
//! [`format`]: format() "fmt::format"

#![stable(feature = "rust1", since = "1.0.0")]

#[stable(feature = "fmt_flags_align", since = "1.28.0")]
pub use core::fmt::Alignment;
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::Error;
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{write, Arguments};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{Binary, Octal};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{Debug, Display};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{Formatter, Result, Write};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{LowerExp, UpperExp};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::fmt::{LowerHex, Pointer, UpperHex};

#[cfg(not(no_global_oom_handling))]
use crate::string;

/// The `format` function takes an [`Arguments`] struct and returns the resulting
/// formatted string.
///
/// The [`Arguments`] instance can be created with the [`format_args!`] macro.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::fmt;
///
/// let s = fmt::format(format_args!("Hello, {}!", "world"));
/// assert_eq!(s, "Hello, world!");
/// ```
///
/// Please note that using [`format!`] might be preferable.
/// Example:
///
/// ```
/// let s = format!("Hello, {}!", "world");
/// assert_eq!(s, "Hello, world!");
/// ```
///
/// [`format_args!`]: core::format_args
/// [`format!`]: crate::format
#[cfg(not(no_global_oom_handling))]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn format(args: Arguments<'_>) -> string::String {
    fn format_inner(args: Arguments<'_>) -> string::String {
        let capacity = args.estimated_capacity();
        let mut output = string::String::with_capacity(capacity);
        output.write_fmt(args).expect("a formatting trait implementation returned an error");
        output
    }

    args.as_str().map_or_else(|| format_inner(args), crate::borrow::ToOwned::to_owned)
}