      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

    // Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! 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"
    //! format!("{} {}", 1, 2);           // => "1 2"
    //! format!("{:04}", 42);             // => "0042" with leading zeros
    //! ```
    //!
    //! 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.
    //!
    //! ## 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 which explicitly name their argument do not affect
    //! parameters which 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 which 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 argument:
    //!
    //! ```
    //! 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"
    //! ```
    //!
    //! It is not valid to put positional parameters (those without names) after
    //! arguments which have names. Like with positional parameters, it is not
    //! valid to provide named parameters that are unused by the format string.
    //!
    //! ## Argument types
    //!
    //! Each argument's type is dictated by the format string.
    //! There are various parameters which require a particular type, however.
    //! An example is the `{:.*}` syntax, which sets the number of decimal places
    //! in floating-point types:
    //!
    //! ```
    //! let formatted_number = format!("{:.*}", 2, 1.234567);
    //!
    //! assert_eq!("1.23", formatted_number)
    //! ```
    //!
    //! If this syntax is used, then the number of characters to print precedes the
    //! actual object being formatted, and the number of characters must have the
    //! type `usize`.
    //!
    //! ## 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`](trait.Display.html)
    //! * `?` ⇒ [`Debug`](trait.Debug.html)
    //! * `o` ⇒ [`Octal`](trait.Octal.html)
    //! * `x` ⇒ [`LowerHex`](trait.LowerHex.html)
    //! * `X` ⇒ [`UpperHex`](trait.UpperHex.html)
    //! * `p` ⇒ [`Pointer`](trait.Pointer.html)
    //! * `b` ⇒ [`Binary`](trait.Binary.html)
    //! * `e` ⇒ [`LowerExp`](trait.LowerExp.html)
    //! * `E` ⇒ [`UpperExp`](trait.UpperExp.html)
    //!
    //! What this means is that any type of argument which implements the
    //! `fmt::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 `f.buf` stream. It is up to each format trait
    //! implementation to correctly adhere to the requested formatting parameters.
    //! The values of these parameters will be listed in the fields 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 `Result<(), std::fmt::Error>`. 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!("{:.*}", decimals, magnitude);
    //!         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!("{:10.3b}", myvector); // => "     5.000"
    //! }
    //! ```
    //!
    //! ### `fmt::Display` vs `fmt::Debug`
    //!
    //! These two formatting traits have distinct purposes:
    //!
    //! - `fmt::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` 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 a &mut io::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
    //! format_args! // described below.
    //! ```
    //!
    //! ### `write!`
    //!
    //! This 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` 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");
    //! ```
    //!
    //! ### `format_args!`
    //!
    //! This is a curious macro which is 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 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.
    //!
    //! # Syntax
    //!
    //! 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 ] '}'
    //! argument := integer | identifier
    //!
    //! format_spec := [[fill]align][sign]['#']['0'][width]['.' precision][type]
    //! fill := character
    //! align := '<' | '^' | '>'
    //! sign := '+' | '-'
    //! width := count
    //! precision := count | '*'
    //! type := identifier | ''
    //! count := parameter | integer
    //! parameter := argument '$'
    //! ```
    //!
    //! # Formatting Parameters
    //!
    //! Each argument being formatted can be transformed by a number of formatting
    //! parameters (corresponding to `format_spec` in the syntax above). These
    //! parameters affect the string representation of what's being formatted. This
    //! syntax draws heavily from Python's, so it may seem a bit familiar.
    //!
    //! ## Fill/Alignment
    //!
    //! The fill character is provided normally in conjunction with the `width`
    //! parameter. This indicates that if the value being formatted is smaller than
    //! `width` some extra characters will be printed around it. The extra
    //! characters are specified by `fill`, and the alignment can be one of the
    //! following options:
    //!
    //! * `<` - the argument is left-aligned in `width` columns
    //! * `^` - the argument is center-aligned in `width` columns
    //! * `>` - the argument is right-aligned in `width` columns
    //!
    //! Note that alignment may not be implemented by some types. A good way
    //! to ensure padding is applied is to format your input, then use this
    //! resulting string to pad your output.
    //!
    //! ## Sign/`#`/`0`
    //!
    //! These can all be interpreted as flags for a particular formatter.
    //!
    //! * `+` - This is intended for numeric types and indicates that the sign
    //!         should always be printed. Positive signs are never printed by
    //!         default, and the negative sign is only printed by default for the
    //!         `Signed` trait. This flag indicates that the correct sign (`+` or `-`)
    //!         should always be printed.
    //! * `-` - Currently not used
    //! * `#` - This flag is indicates that the "alternate" form of printing should
    //!         be used. The alternate forms are:
    //!     * `#?` - pretty-print the `Debug` formatting
    //!     * `#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 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 zeroes are always placed after the sign (if any)
    //!         and before the digits. When used together with the `#` flag, a similar
    //!         rule applies: padding zeroes are inserted after the prefix but before
    //!         the digits.
    //!
    //! ## Width
    //!
    //! 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.
    //!
    //! The default fill/alignment for non-numerics is a space and left-aligned. The
    //! defaults for numeric formatters is also a space but with right-alignment. If
    //! the `0` flag is specified for numerics, then the implicit fill character is
    //! `0`.
    //!
    //! The value for the width can also be provided as a `usize` in the list of
    //! parameters by using the dollar syntax indicating that the second argument is
    //! a `usize` specifying the width, for example:
    //!
    //! ```
    //! // 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);
    //! ```
    //!
    //! 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.
    //!
    //! ## 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$`:
    //!
    //!    use format *argument* `N` (which must be a `usize`) as the precision.
    //!
    //! 3. An asterisk `.*`:
    //!
    //!    `.*` means that this `{...}` is associated with *two* format inputs rather than one: the
    //!    first input holds the `usize` precision, and the second holds the value to print.  Note that
    //!    in this case, if one uses the format string `{<arg>:<spec>.*}`, then the `<arg>` part refers
    //!    to the *value* to print, and the `precision` must come in the input preceding `<arg>`.
    //!
    //! For example, the following calls all print the same thing `Hello x is 0.01000`:
    //!
    //! ```
    //! // Hello {arg 0 ("x")} is {arg 1 (0.01) with precision specified inline (5)}
    //! println!("Hello {0} is {1:.5}", "x", 0.01);
    //!
    //! // Hello {arg 1 ("x")} is {arg 2 (0.01) with precision specified in arg 0 (5)}
    //! println!("Hello {1} is {2:.0$}", 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$}", "x", 5, 0.01);
    //!
    //! // Hello {next arg ("x")} is {second of next two args (0.01) with precision
    //! //                          specified in first of next two args (5)}
    //! println!("Hello {} is {:.*}",    "x", 5, 0.01);
    //!
    //! // Hello {next arg ("x")} is {arg 2 (0.01) with precision
    //! //                          specified in its predecessor (5)}
    //! println!("Hello {} is {2:.*}",   "x", 5, 0.01);
    //!
    //! // Hello {next arg ("x")} is {arg "number" (0.01) with precision specified
    //! //                          in arg "prec" (5)}
    //! println!("Hello {} is {number:.prec$}", "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 two significantly different things:
    //!
    //! ```text
    //! Hello, `1234.560` has 3 fractional digits
    //! Hello, `123` has 3 characters
    //! Hello, `     123` has 3 right-aligned characters
    //! ```
    //!
    //! # 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 `}}`.

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

    #[unstable(feature = "fmt_internals", issue = "0")]
    pub use core::fmt::rt;
    #[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::{Octal, Binary};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::fmt::{Display, Debug};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::fmt::{LowerHex, UpperHex, Pointer};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::fmt::{LowerExp, UpperExp};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::fmt::Error;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::fmt::{ArgumentV1, Arguments, write};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::fmt::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};

    use 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!`][format!] might be preferrable.
    /// Example:
    ///
    /// ```
    /// let s = format!("Hello, {}!", "world");
    /// assert_eq!(s, "Hello, world!");
    /// ```
    ///
    /// [format!]: ../macro.format.html
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn format(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
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result
+
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)