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1a4d82fc | 1 | // Copyright 2014 The Rust Project Developers. See the COPYRIGHT |
970d7e83 LB |
2 | // file at the top-level directory of this distribution and at |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
1a4d82fc JJ |
11 | //! Standard library macros |
12 | //! | |
13 | //! This modules contains a set of macros which are exported from the standard | |
14 | //! library. Each macro is available for use when linking against the standard | |
15 | //! library. | |
970d7e83 | 16 | |
bd371182 | 17 | /// The entry point for panic of Rust threads. |
9346a6ac | 18 | /// |
ea8adc8c XL |
19 | /// This allows a program to to terminate immediately and provide feedback |
20 | /// to the caller of the program. `panic!` should be used when a program reaches | |
21 | /// an unrecoverable problem. | |
22 | /// | |
23 | /// This macro is the perfect way to assert conditions in example code and in | |
24 | /// tests. `panic!` is closely tied with the `unwrap` method of both [`Option`] | |
25 | /// and [`Result`][runwrap] enums. Both implementations call `panic!` when they are set | |
26 | /// to None or Err variants. | |
27 | /// | |
bd371182 | 28 | /// This macro is used to inject panic into a Rust thread, causing the thread to |
a7813a04 XL |
29 | /// panic entirely. Each thread's panic can be reaped as the `Box<Any>` type, |
30 | /// and the single-argument form of the `panic!` macro will be the value which | |
31 | /// is transmitted. | |
9346a6ac | 32 | /// |
ea8adc8c XL |
33 | /// [`Result`] enum is often a better solution for recovering from errors than |
34 | /// using the `panic!` macro. This macro should be used to avoid proceeding using | |
35 | /// incorrect values, such as from external sources. Detailed information about | |
36 | /// error handling is found in the [book]. | |
37 | /// | |
9346a6ac | 38 | /// The multi-argument form of this macro panics with a string and has the |
ea8adc8c XL |
39 | /// [`format!`] syntax for building a string. |
40 | /// | |
41 | /// [runwrap]: ../std/result/enum.Result.html#method.unwrap | |
42 | /// [`Option`]: ../std/option/enum.Option.html#method.unwrap | |
43 | /// [`Result`]: ../std/result/enum.Result.html | |
44 | /// [`format!`]: ../std/macro.format.html | |
45 | /// [book]: ../book/second-edition/ch09-01-unrecoverable-errors-with-panic.html | |
9346a6ac | 46 | /// |
041b39d2 XL |
47 | /// # Current implementation |
48 | /// | |
49 | /// If the main thread panics it will terminate all your threads and end your | |
50 | /// program with code `101`. | |
51 | /// | |
9346a6ac AL |
52 | /// # Examples |
53 | /// | |
54 | /// ```should_panic | |
55 | /// # #![allow(unreachable_code)] | |
56 | /// panic!(); | |
57 | /// panic!("this is a terrible mistake!"); | |
58 | /// panic!(4); // panic with the value of 4 to be collected elsewhere | |
59 | /// panic!("this is a {} {message}", "fancy", message = "message"); | |
60 | /// ``` | |
61 | #[macro_export] | |
62 | #[stable(feature = "rust1", since = "1.0.0")] | |
63 | #[allow_internal_unstable] | |
9346a6ac AL |
64 | macro_rules! panic { |
65 | () => ({ | |
66 | panic!("explicit panic") | |
67 | }); | |
68 | ($msg:expr) => ({ | |
ea8adc8c | 69 | $crate::rt::begin_panic($msg, &(file!(), line!(), __rust_unstable_column!())) |
9346a6ac | 70 | }); |
0531ce1d XL |
71 | ($msg:expr,) => ({ |
72 | panic!($msg) | |
73 | }); | |
9346a6ac | 74 | ($fmt:expr, $($arg:tt)+) => ({ |
ea8adc8c XL |
75 | $crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+), |
76 | &(file!(), line!(), __rust_unstable_column!())) | |
1a4d82fc JJ |
77 | }); |
78 | } | |
79 | ||
c34b1796 AL |
80 | /// Macro for printing to the standard output. |
81 | /// | |
ea8adc8c | 82 | /// Equivalent to the [`println!`] macro except that a newline is not printed at |
1a4d82fc | 83 | /// the end of the message. |
c34b1796 AL |
84 | /// |
85 | /// Note that stdout is frequently line-buffered by default so it may be | |
ea8adc8c | 86 | /// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted |
c34b1796 | 87 | /// immediately. |
e9174d1e | 88 | /// |
7cac9316 | 89 | /// Use `print!` only for the primary output of your program. Use |
ea8adc8c XL |
90 | /// [`eprint!`] instead to print error and progress messages. |
91 | /// | |
92 | /// [`println!`]: ../std/macro.println.html | |
93 | /// [flush]: ../std/io/trait.Write.html#tymethod.flush | |
94 | /// [`eprint!`]: ../std/macro.eprint.html | |
7cac9316 | 95 | /// |
b039eaaf SL |
96 | /// # Panics |
97 | /// | |
98 | /// Panics if writing to `io::stdout()` fails. | |
99 | /// | |
e9174d1e SL |
100 | /// # Examples |
101 | /// | |
102 | /// ``` | |
103 | /// use std::io::{self, Write}; | |
104 | /// | |
105 | /// print!("this "); | |
106 | /// print!("will "); | |
107 | /// print!("be "); | |
108 | /// print!("on "); | |
109 | /// print!("the "); | |
110 | /// print!("same "); | |
111 | /// print!("line "); | |
112 | /// | |
113 | /// io::stdout().flush().unwrap(); | |
114 | /// | |
115 | /// print!("this string has a newline, why not choose println! instead?\n"); | |
116 | /// | |
117 | /// io::stdout().flush().unwrap(); | |
118 | /// ``` | |
1a4d82fc | 119 | #[macro_export] |
85aaf69f | 120 | #[stable(feature = "rust1", since = "1.0.0")] |
c34b1796 | 121 | #[allow_internal_unstable] |
1a4d82fc | 122 | macro_rules! print { |
c34b1796 | 123 | ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*))); |
1a4d82fc | 124 | } |
970d7e83 | 125 | |
ea8adc8c XL |
126 | /// Macro for printing to the standard output, with a newline. |
127 | /// | |
128 | /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone | |
5bcae85e | 129 | /// (no additional CARRIAGE RETURN (`\r`/`U+000D`). |
1a4d82fc | 130 | /// |
ea8adc8c XL |
131 | /// Use the [`format!`] syntax to write data to the standard output. |
132 | /// See [`std::fmt`] for more information. | |
1a4d82fc | 133 | /// |
7cac9316 | 134 | /// Use `println!` only for the primary output of your program. Use |
ea8adc8c | 135 | /// [`eprintln!`] instead to print error and progress messages. |
7cac9316 | 136 | /// |
ea8adc8c XL |
137 | /// [`format!`]: ../std/macro.format.html |
138 | /// [`std::fmt`]: ../std/fmt/index.html | |
139 | /// [`eprintln!`]: ../std/macro.eprint.html | |
b039eaaf SL |
140 | /// # Panics |
141 | /// | |
7cac9316 | 142 | /// Panics if writing to `io::stdout` fails. |
b039eaaf | 143 | /// |
c34b1796 | 144 | /// # Examples |
1a4d82fc JJ |
145 | /// |
146 | /// ``` | |
32a655c1 | 147 | /// println!(); // prints just a newline |
1a4d82fc JJ |
148 | /// println!("hello there!"); |
149 | /// println!("format {} arguments", "some"); | |
150 | /// ``` | |
151 | #[macro_export] | |
85aaf69f | 152 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 153 | macro_rules! println { |
c30ab7b3 | 154 | () => (print!("\n")); |
c34b1796 AL |
155 | ($fmt:expr) => (print!(concat!($fmt, "\n"))); |
156 | ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*)); | |
1a4d82fc JJ |
157 | } |
158 | ||
7cac9316 XL |
159 | /// Macro for printing to the standard error. |
160 | /// | |
ea8adc8c XL |
161 | /// Equivalent to the [`print!`] macro, except that output goes to |
162 | /// [`io::stderr`] instead of `io::stdout`. See [`print!`] for | |
7cac9316 XL |
163 | /// example usage. |
164 | /// | |
165 | /// Use `eprint!` only for error and progress messages. Use `print!` | |
166 | /// instead for the primary output of your program. | |
167 | /// | |
ea8adc8c XL |
168 | /// [`io::stderr`]: ../std/io/struct.Stderr.html |
169 | /// [`print!`]: ../std/macro.print.html | |
170 | /// | |
7cac9316 XL |
171 | /// # Panics |
172 | /// | |
173 | /// Panics if writing to `io::stderr` fails. | |
ea8adc8c XL |
174 | /// |
175 | /// # Examples | |
176 | /// | |
177 | /// ``` | |
178 | /// eprint!("Error: Could not complete task"); | |
179 | /// ``` | |
7cac9316 XL |
180 | #[macro_export] |
181 | #[stable(feature = "eprint", since = "1.19.0")] | |
182 | #[allow_internal_unstable] | |
183 | macro_rules! eprint { | |
184 | ($($arg:tt)*) => ($crate::io::_eprint(format_args!($($arg)*))); | |
185 | } | |
186 | ||
187 | /// Macro for printing to the standard error, with a newline. | |
188 | /// | |
ea8adc8c XL |
189 | /// Equivalent to the [`println!`] macro, except that output goes to |
190 | /// [`io::stderr`] instead of `io::stdout`. See [`println!`] for | |
7cac9316 XL |
191 | /// example usage. |
192 | /// | |
193 | /// Use `eprintln!` only for error and progress messages. Use `println!` | |
194 | /// instead for the primary output of your program. | |
195 | /// | |
ea8adc8c XL |
196 | /// [`io::stderr`]: ../std/io/struct.Stderr.html |
197 | /// [`println!`]: ../std/macro.println.html | |
198 | /// | |
7cac9316 XL |
199 | /// # Panics |
200 | /// | |
201 | /// Panics if writing to `io::stderr` fails. | |
ea8adc8c XL |
202 | /// |
203 | /// # Examples | |
204 | /// | |
205 | /// ``` | |
206 | /// eprintln!("Error: Could not complete task"); | |
207 | /// ``` | |
7cac9316 XL |
208 | #[macro_export] |
209 | #[stable(feature = "eprint", since = "1.19.0")] | |
210 | macro_rules! eprintln { | |
211 | () => (eprint!("\n")); | |
212 | ($fmt:expr) => (eprint!(concat!($fmt, "\n"))); | |
213 | ($fmt:expr, $($arg:tt)*) => (eprint!(concat!($fmt, "\n"), $($arg)*)); | |
214 | } | |
215 | ||
1a4d82fc JJ |
216 | /// A macro to select an event from a number of receivers. |
217 | /// | |
218 | /// This macro is used to wait for the first event to occur on a number of | |
219 | /// receivers. It places no restrictions on the types of receivers given to | |
220 | /// this macro, this can be viewed as a heterogeneous select. | |
221 | /// | |
85aaf69f | 222 | /// # Examples |
1a4d82fc JJ |
223 | /// |
224 | /// ``` | |
c1a9b12d SL |
225 | /// #![feature(mpsc_select)] |
226 | /// | |
85aaf69f SL |
227 | /// use std::thread; |
228 | /// use std::sync::mpsc; | |
1a4d82fc | 229 | /// |
85aaf69f | 230 | /// // two placeholder functions for now |
bd371182 | 231 | /// fn long_running_thread() {} |
85aaf69f | 232 | /// fn calculate_the_answer() -> u32 { 42 } |
1a4d82fc | 233 | /// |
85aaf69f SL |
234 | /// let (tx1, rx1) = mpsc::channel(); |
235 | /// let (tx2, rx2) = mpsc::channel(); | |
236 | /// | |
bd371182 | 237 | /// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); }); |
85aaf69f | 238 | /// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); }); |
1a4d82fc | 239 | /// |
d9579d0f | 240 | /// select! { |
bd371182 | 241 | /// _ = rx1.recv() => println!("the long running thread finished first"), |
1a4d82fc JJ |
242 | /// answer = rx2.recv() => { |
243 | /// println!("the answer was: {}", answer.unwrap()); | |
244 | /// } | |
d9579d0f AL |
245 | /// } |
246 | /// # drop(rx1.recv()); | |
247 | /// # drop(rx2.recv()); | |
1a4d82fc JJ |
248 | /// ``` |
249 | /// | |
250 | /// For more information about select, see the `std::sync::mpsc::Select` structure. | |
251 | #[macro_export] | |
e9174d1e | 252 | #[unstable(feature = "mpsc_select", issue = "27800")] |
1a4d82fc JJ |
253 | macro_rules! select { |
254 | ( | |
255 | $($name:pat = $rx:ident.$meth:ident() => $code:expr),+ | |
256 | ) => ({ | |
257 | use $crate::sync::mpsc::Select; | |
258 | let sel = Select::new(); | |
259 | $( let mut $rx = sel.handle(&$rx); )+ | |
260 | unsafe { | |
261 | $( $rx.add(); )+ | |
970d7e83 | 262 | } |
1a4d82fc JJ |
263 | let ret = sel.wait(); |
264 | $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+ | |
265 | { unreachable!() } | |
266 | }) | |
267 | } | |
268 | ||
e9174d1e SL |
269 | #[cfg(test)] |
270 | macro_rules! assert_approx_eq { | |
271 | ($a:expr, $b:expr) => ({ | |
272 | let (a, b) = (&$a, &$b); | |
273 | assert!((*a - *b).abs() < 1.0e-6, | |
274 | "{} is not approximately equal to {}", *a, *b); | |
275 | }) | |
276 | } | |
277 | ||
1a4d82fc JJ |
278 | /// Built-in macros to the compiler itself. |
279 | /// | |
280 | /// These macros do not have any corresponding definition with a `macro_rules!` | |
281 | /// macro, but are documented here. Their implementations can be found hardcoded | |
282 | /// into libsyntax itself. | |
283 | #[cfg(dox)] | |
284 | pub mod builtin { | |
041b39d2 XL |
285 | |
286 | /// Unconditionally causes compilation to fail with the given error message when encountered. | |
287 | /// | |
ff7c6d11 | 288 | /// This macro should be used when a crate uses a conditional compilation strategy to provide |
2c00a5a8 | 289 | /// better error messages for erroneous conditions. |
041b39d2 | 290 | /// |
ff7c6d11 XL |
291 | /// # Examples |
292 | /// | |
293 | /// Two such examples are macros and `#[cfg]` environments. | |
294 | /// | |
295 | /// Emit better compiler error if a macro is passed invalid values. | |
296 | /// | |
297 | /// ```compile_fail | |
298 | /// macro_rules! give_me_foo_or_bar { | |
299 | /// (foo) => {}; | |
300 | /// (bar) => {}; | |
301 | /// ($x:ident) => { | |
302 | /// compile_error!("This macro only accepts `foo` or `bar`"); | |
303 | /// } | |
304 | /// } | |
305 | /// | |
306 | /// give_me_foo_or_bar!(neither); | |
307 | /// // ^ will fail at compile time with message "This macro only accepts `foo` or `bar`" | |
308 | /// ``` | |
309 | /// | |
310 | /// Emit compiler error if one of a number of features isn't available. | |
311 | /// | |
312 | /// ```compile_fail | |
313 | /// #[cfg(not(any(feature = "foo", feature = "bar")))] | |
314 | /// compile_error!("Either feature \"foo\" or \"bar\" must be enabled for this crate.") | |
315 | /// ``` | |
041b39d2 XL |
316 | #[stable(feature = "compile_error_macro", since = "1.20.0")] |
317 | #[macro_export] | |
0531ce1d XL |
318 | macro_rules! compile_error { |
319 | ($msg:expr) => ({ /* compiler built-in */ }); | |
320 | ($msg:expr,) => ({ /* compiler built-in */ }); | |
321 | } | |
041b39d2 | 322 | |
1a4d82fc JJ |
323 | /// The core macro for formatted string creation & output. |
324 | /// | |
ea8adc8c XL |
325 | /// This macro functions by taking a formatting string literal containing |
326 | /// `{}` for each additional argument passed. `format_args!` prepares the | |
327 | /// additional parameters to ensure the output can be interpreted as a string | |
328 | /// and canonicalizes the arguments into a single type. Any value that implements | |
329 | /// the [`Display`] trait can be passed to `format_args!`, as can any | |
330 | /// [`Debug`] implementation be passed to a `{:?}` within the formatting string. | |
331 | /// | |
9e0c209e | 332 | /// This macro produces a value of type [`fmt::Arguments`]. This value can be |
ea8adc8c | 333 | /// passed to the macros within [`std::fmt`] for performing useful redirection. |
9e0c209e | 334 | /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are |
ea8adc8c XL |
335 | /// proxied through this one. `format_args!`, unlike its derived macros, avoids |
336 | /// heap allocations. | |
1a4d82fc | 337 | /// |
0531ce1d XL |
338 | /// You can use the [`fmt::Arguments`] value that `format_args!` returns |
339 | /// in `Debug` and `Display` contexts as seen below. The example also shows | |
340 | /// that `Debug` and `Display` format to the same thing: the interpolated | |
341 | /// format string in `format_args!`. | |
342 | /// | |
343 | /// ```rust | |
83c7162d XL |
344 | /// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2)); |
345 | /// let display = format!("{}", format_args!("{} foo {:?}", 1, 2)); | |
0531ce1d XL |
346 | /// assert_eq!("1 foo 2", display); |
347 | /// assert_eq!(display, debug); | |
348 | /// ``` | |
349 | /// | |
9e0c209e SL |
350 | /// For more information, see the documentation in [`std::fmt`]. |
351 | /// | |
ea8adc8c XL |
352 | /// [`Display`]: ../std/fmt/trait.Display.html |
353 | /// [`Debug`]: ../std/fmt/trait.Debug.html | |
9e0c209e SL |
354 | /// [`fmt::Arguments`]: ../std/fmt/struct.Arguments.html |
355 | /// [`std::fmt`]: ../std/fmt/index.html | |
356 | /// [`format!`]: ../std/macro.format.html | |
357 | /// [`write!`]: ../std/macro.write.html | |
358 | /// [`println!`]: ../std/macro.println.html | |
1a4d82fc | 359 | /// |
c34b1796 | 360 | /// # Examples |
1a4d82fc | 361 | /// |
c34b1796 | 362 | /// ``` |
1a4d82fc JJ |
363 | /// use std::fmt; |
364 | /// | |
365 | /// let s = fmt::format(format_args!("hello {}", "world")); | |
366 | /// assert_eq!(s, format!("hello {}", "world")); | |
367 | /// | |
368 | /// ``` | |
92a42be0 | 369 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 370 | #[macro_export] |
ff7c6d11 XL |
371 | macro_rules! format_args { |
372 | ($fmt:expr) => ({ /* compiler built-in */ }); | |
373 | ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ }); | |
374 | } | |
1a4d82fc JJ |
375 | |
376 | /// Inspect an environment variable at compile time. | |
377 | /// | |
378 | /// This macro will expand to the value of the named environment variable at | |
379 | /// compile time, yielding an expression of type `&'static str`. | |
380 | /// | |
381 | /// If the environment variable is not defined, then a compilation error | |
ea8adc8c | 382 | /// will be emitted. To not emit a compile error, use the [`option_env!`] |
1a4d82fc JJ |
383 | /// macro instead. |
384 | /// | |
ea8adc8c XL |
385 | /// [`option_env!`]: ../std/macro.option_env.html |
386 | /// | |
c34b1796 | 387 | /// # Examples |
1a4d82fc | 388 | /// |
c34b1796 | 389 | /// ``` |
1a4d82fc JJ |
390 | /// let path: &'static str = env!("PATH"); |
391 | /// println!("the $PATH variable at the time of compiling was: {}", path); | |
392 | /// ``` | |
92a42be0 | 393 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 394 | #[macro_export] |
ff7c6d11 XL |
395 | macro_rules! env { |
396 | ($name:expr) => ({ /* compiler built-in */ }); | |
397 | ($name:expr,) => ({ /* compiler built-in */ }); | |
398 | } | |
1a4d82fc JJ |
399 | |
400 | /// Optionally inspect an environment variable at compile time. | |
401 | /// | |
402 | /// If the named environment variable is present at compile time, this will | |
403 | /// expand into an expression of type `Option<&'static str>` whose value is | |
404 | /// `Some` of the value of the environment variable. If the environment | |
ea8adc8c XL |
405 | /// variable is not present, then this will expand to `None`. See |
406 | /// [`Option<T>`][option] for more information on this type. | |
1a4d82fc JJ |
407 | /// |
408 | /// A compile time error is never emitted when using this macro regardless | |
409 | /// of whether the environment variable is present or not. | |
410 | /// | |
ea8adc8c XL |
411 | /// [option]: ../std/option/enum.Option.html |
412 | /// | |
c34b1796 | 413 | /// # Examples |
1a4d82fc | 414 | /// |
c34b1796 | 415 | /// ``` |
1a4d82fc JJ |
416 | /// let key: Option<&'static str> = option_env!("SECRET_KEY"); |
417 | /// println!("the secret key might be: {:?}", key); | |
418 | /// ``` | |
92a42be0 | 419 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 420 | #[macro_export] |
0531ce1d XL |
421 | macro_rules! option_env { |
422 | ($name:expr) => ({ /* compiler built-in */ }); | |
423 | ($name:expr,) => ({ /* compiler built-in */ }); | |
424 | } | |
1a4d82fc JJ |
425 | |
426 | /// Concatenate identifiers into one identifier. | |
427 | /// | |
428 | /// This macro takes any number of comma-separated identifiers, and | |
429 | /// concatenates them all into one, yielding an expression which is a new | |
430 | /// identifier. Note that hygiene makes it such that this macro cannot | |
7453a54e SL |
431 | /// capture local variables. Also, as a general rule, macros are only |
432 | /// allowed in item, statement or expression position. That means while | |
433 | /// you may use this macro for referring to existing variables, functions or | |
434 | /// modules etc, you cannot define a new one with it. | |
1a4d82fc | 435 | /// |
85aaf69f | 436 | /// # Examples |
1a4d82fc JJ |
437 | /// |
438 | /// ``` | |
439 | /// #![feature(concat_idents)] | |
440 | /// | |
441 | /// # fn main() { | |
85aaf69f | 442 | /// fn foobar() -> u32 { 23 } |
1a4d82fc JJ |
443 | /// |
444 | /// let f = concat_idents!(foo, bar); | |
445 | /// println!("{}", f()); | |
7453a54e SL |
446 | /// |
447 | /// // fn concat_idents!(new, fun, name) { } // not usable in this way! | |
1a4d82fc JJ |
448 | /// # } |
449 | /// ``` | |
c30ab7b3 | 450 | #[unstable(feature = "concat_idents_macro", issue = "29599")] |
1a4d82fc JJ |
451 | #[macro_export] |
452 | macro_rules! concat_idents { | |
83c7162d XL |
453 | ($($e:ident),+) => ({ /* compiler built-in */ }); |
454 | ($($e:ident,)+) => ({ /* compiler built-in */ }); | |
1a4d82fc JJ |
455 | } |
456 | ||
457 | /// Concatenates literals into a static string slice. | |
458 | /// | |
459 | /// This macro takes any number of comma-separated literals, yielding an | |
460 | /// expression of type `&'static str` which represents all of the literals | |
461 | /// concatenated left-to-right. | |
462 | /// | |
463 | /// Integer and floating point literals are stringified in order to be | |
464 | /// concatenated. | |
465 | /// | |
c34b1796 | 466 | /// # Examples |
1a4d82fc JJ |
467 | /// |
468 | /// ``` | |
85aaf69f | 469 | /// let s = concat!("test", 10, 'b', true); |
1a4d82fc JJ |
470 | /// assert_eq!(s, "test10btrue"); |
471 | /// ``` | |
92a42be0 | 472 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 473 | #[macro_export] |
ff7c6d11 XL |
474 | macro_rules! concat { |
475 | ($($e:expr),*) => ({ /* compiler built-in */ }); | |
476 | ($($e:expr,)*) => ({ /* compiler built-in */ }); | |
477 | } | |
1a4d82fc JJ |
478 | |
479 | /// A macro which expands to the line number on which it was invoked. | |
480 | /// | |
ea8adc8c XL |
481 | /// With [`column!`] and [`file!`], these macros provide debugging information for |
482 | /// developers about the location within the source. | |
483 | /// | |
ff7c6d11 XL |
484 | /// The expanded expression has type `u32` and is 1-based, so the first line |
485 | /// in each file evaluates to 1, the second to 2, etc. This is consistent | |
486 | /// with error messages by common compilers or popular editors. | |
0531ce1d | 487 | /// The returned line is *not necessarily* the line of the `line!` invocation itself, |
ff7c6d11 XL |
488 | /// but rather the first macro invocation leading up to the invocation |
489 | /// of the `line!` macro. | |
1a4d82fc | 490 | /// |
ea8adc8c XL |
491 | /// [`column!`]: macro.column.html |
492 | /// [`file!`]: macro.file.html | |
493 | /// | |
c34b1796 | 494 | /// # Examples |
1a4d82fc JJ |
495 | /// |
496 | /// ``` | |
497 | /// let current_line = line!(); | |
498 | /// println!("defined on line: {}", current_line); | |
499 | /// ``` | |
92a42be0 | 500 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
501 | #[macro_export] |
502 | macro_rules! line { () => ({ /* compiler built-in */ }) } | |
503 | ||
504 | /// A macro which expands to the column number on which it was invoked. | |
505 | /// | |
ea8adc8c XL |
506 | /// With [`line!`] and [`file!`], these macros provide debugging information for |
507 | /// developers about the location within the source. | |
508 | /// | |
ff7c6d11 XL |
509 | /// The expanded expression has type `u32` and is 1-based, so the first column |
510 | /// in each line evaluates to 1, the second to 2, etc. This is consistent | |
511 | /// with error messages by common compilers or popular editors. | |
0531ce1d | 512 | /// The returned column is *not necessarily* the line of the `column!` invocation itself, |
ff7c6d11 XL |
513 | /// but rather the first macro invocation leading up to the invocation |
514 | /// of the `column!` macro. | |
ea8adc8c XL |
515 | /// |
516 | /// [`line!`]: macro.line.html | |
517 | /// [`file!`]: macro.file.html | |
1a4d82fc | 518 | /// |
c34b1796 | 519 | /// # Examples |
1a4d82fc JJ |
520 | /// |
521 | /// ``` | |
522 | /// let current_col = column!(); | |
523 | /// println!("defined on column: {}", current_col); | |
524 | /// ``` | |
92a42be0 | 525 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
526 | #[macro_export] |
527 | macro_rules! column { () => ({ /* compiler built-in */ }) } | |
528 | ||
529 | /// A macro which expands to the file name from which it was invoked. | |
530 | /// | |
ea8adc8c XL |
531 | /// With [`line!`] and [`column!`], these macros provide debugging information for |
532 | /// developers about the location within the source. | |
533 | /// | |
534 | /// | |
1a4d82fc | 535 | /// The expanded expression has type `&'static str`, and the returned file |
ea8adc8c XL |
536 | /// is not the invocation of the `file!` macro itself, but rather the |
537 | /// first macro invocation leading up to the invocation of the `file!` | |
1a4d82fc JJ |
538 | /// macro. |
539 | /// | |
ea8adc8c XL |
540 | /// [`line!`]: macro.line.html |
541 | /// [`column!`]: macro.column.html | |
542 | /// | |
c34b1796 | 543 | /// # Examples |
1a4d82fc JJ |
544 | /// |
545 | /// ``` | |
546 | /// let this_file = file!(); | |
547 | /// println!("defined in file: {}", this_file); | |
548 | /// ``` | |
92a42be0 | 549 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
550 | #[macro_export] |
551 | macro_rules! file { () => ({ /* compiler built-in */ }) } | |
552 | ||
abe05a73 | 553 | /// A macro which stringifies its arguments. |
1a4d82fc JJ |
554 | /// |
555 | /// This macro will yield an expression of type `&'static str` which is the | |
556 | /// stringification of all the tokens passed to the macro. No restrictions | |
557 | /// are placed on the syntax of the macro invocation itself. | |
558 | /// | |
7453a54e SL |
559 | /// Note that the expanded results of the input tokens may change in the |
560 | /// future. You should be careful if you rely on the output. | |
561 | /// | |
c34b1796 | 562 | /// # Examples |
1a4d82fc JJ |
563 | /// |
564 | /// ``` | |
565 | /// let one_plus_one = stringify!(1 + 1); | |
566 | /// assert_eq!(one_plus_one, "1 + 1"); | |
567 | /// ``` | |
92a42be0 | 568 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 569 | #[macro_export] |
abe05a73 | 570 | macro_rules! stringify { ($($t:tt)*) => ({ /* compiler built-in */ }) } |
1a4d82fc JJ |
571 | |
572 | /// Includes a utf8-encoded file as a string. | |
573 | /// | |
c30ab7b3 SL |
574 | /// The file is located relative to the current file. (similarly to how |
575 | /// modules are found) | |
576 | /// | |
1a4d82fc | 577 | /// This macro will yield an expression of type `&'static str` which is the |
c30ab7b3 | 578 | /// contents of the file. |
1a4d82fc | 579 | /// |
c34b1796 | 580 | /// # Examples |
1a4d82fc | 581 | /// |
3b2f2976 XL |
582 | /// Assume there are two files in the same directory with the following |
583 | /// contents: | |
584 | /// | |
585 | /// File 'spanish.in': | |
586 | /// | |
587 | /// ```text | |
588 | /// adiรณs | |
589 | /// ``` | |
590 | /// | |
591 | /// File 'main.rs': | |
592 | /// | |
041b39d2 | 593 | /// ```ignore (cannot-doctest-external-file-dependency) |
3b2f2976 XL |
594 | /// fn main() { |
595 | /// let my_str = include_str!("spanish.in"); | |
596 | /// assert_eq!(my_str, "adiรณs\n"); | |
597 | /// print!("{}", my_str); | |
598 | /// } | |
1a4d82fc | 599 | /// ``` |
3b2f2976 XL |
600 | /// |
601 | /// Compiling 'main.rs' and running the resulting binary will print "adiรณs". | |
92a42be0 | 602 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 603 | #[macro_export] |
0531ce1d XL |
604 | macro_rules! include_str { |
605 | ($file:expr) => ({ /* compiler built-in */ }); | |
606 | ($file:expr,) => ({ /* compiler built-in */ }); | |
607 | } | |
1a4d82fc | 608 | |
e9174d1e | 609 | /// Includes a file as a reference to a byte array. |
1a4d82fc | 610 | /// |
c30ab7b3 SL |
611 | /// The file is located relative to the current file. (similarly to how |
612 | /// modules are found) | |
613 | /// | |
e9174d1e | 614 | /// This macro will yield an expression of type `&'static [u8; N]` which is |
c30ab7b3 | 615 | /// the contents of the file. |
1a4d82fc | 616 | /// |
c34b1796 | 617 | /// # Examples |
1a4d82fc | 618 | /// |
3b2f2976 XL |
619 | /// Assume there are two files in the same directory with the following |
620 | /// contents: | |
621 | /// | |
622 | /// File 'spanish.in': | |
623 | /// | |
624 | /// ```text | |
625 | /// adiรณs | |
626 | /// ``` | |
627 | /// | |
628 | /// File 'main.rs': | |
629 | /// | |
041b39d2 | 630 | /// ```ignore (cannot-doctest-external-file-dependency) |
3b2f2976 XL |
631 | /// fn main() { |
632 | /// let bytes = include_bytes!("spanish.in"); | |
633 | /// assert_eq!(bytes, b"adi\xc3\xb3s\n"); | |
634 | /// print!("{}", String::from_utf8_lossy(bytes)); | |
635 | /// } | |
1a4d82fc | 636 | /// ``` |
3b2f2976 XL |
637 | /// |
638 | /// Compiling 'main.rs' and running the resulting binary will print "adiรณs". | |
92a42be0 | 639 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 640 | #[macro_export] |
0531ce1d XL |
641 | macro_rules! include_bytes { |
642 | ($file:expr) => ({ /* compiler built-in */ }); | |
643 | ($file:expr,) => ({ /* compiler built-in */ }); | |
644 | } | |
1a4d82fc JJ |
645 | |
646 | /// Expands to a string that represents the current module path. | |
647 | /// | |
648 | /// The current module path can be thought of as the hierarchy of modules | |
649 | /// leading back up to the crate root. The first component of the path | |
650 | /// returned is the name of the crate currently being compiled. | |
651 | /// | |
c34b1796 | 652 | /// # Examples |
1a4d82fc | 653 | /// |
c34b1796 | 654 | /// ``` |
1a4d82fc JJ |
655 | /// mod test { |
656 | /// pub fn foo() { | |
657 | /// assert!(module_path!().ends_with("test")); | |
658 | /// } | |
659 | /// } | |
660 | /// | |
661 | /// test::foo(); | |
662 | /// ``` | |
92a42be0 | 663 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
664 | #[macro_export] |
665 | macro_rules! module_path { () => ({ /* compiler built-in */ }) } | |
666 | ||
ff7c6d11 | 667 | /// Boolean evaluation of configuration flags, at compile-time. |
1a4d82fc JJ |
668 | /// |
669 | /// In addition to the `#[cfg]` attribute, this macro is provided to allow | |
670 | /// boolean expression evaluation of configuration flags. This frequently | |
671 | /// leads to less duplicated code. | |
672 | /// | |
92a42be0 | 673 | /// The syntax given to this macro is the same syntax as [the `cfg` |
041b39d2 | 674 | /// attribute](../book/first-edition/conditional-compilation.html). |
1a4d82fc | 675 | /// |
c34b1796 | 676 | /// # Examples |
1a4d82fc | 677 | /// |
c34b1796 | 678 | /// ``` |
1a4d82fc JJ |
679 | /// let my_directory = if cfg!(windows) { |
680 | /// "windows-specific-directory" | |
681 | /// } else { | |
682 | /// "unix-directory" | |
683 | /// }; | |
684 | /// ``` | |
92a42be0 | 685 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 686 | #[macro_export] |
92a42be0 | 687 | macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) } |
c34b1796 | 688 | |
c30ab7b3 SL |
689 | /// Parse a file as an expression or an item according to the context. |
690 | /// | |
32a655c1 SL |
691 | /// The file is located relative to the current file (similarly to how |
692 | /// modules are found). | |
c34b1796 | 693 | /// |
c30ab7b3 SL |
694 | /// Using this macro is often a bad idea, because if the file is |
695 | /// parsed as an expression, it is going to be placed in the | |
32a655c1 | 696 | /// surrounding code unhygienically. This could result in variables |
c30ab7b3 SL |
697 | /// or functions being different from what the file expected if |
698 | /// there are variables or functions that have the same name in | |
699 | /// the current file. | |
c34b1796 AL |
700 | /// |
701 | /// # Examples | |
702 | /// | |
32a655c1 SL |
703 | /// Assume there are two files in the same directory with the following |
704 | /// contents: | |
705 | /// | |
3b2f2976 | 706 | /// File 'monkeys.in': |
32a655c1 | 707 | /// |
041b39d2 | 708 | /// ```ignore (only-for-syntax-highlight) |
3b2f2976 XL |
709 | /// ['๐', '๐', '๐'] |
710 | /// .iter() | |
711 | /// .cycle() | |
712 | /// .take(6) | |
713 | /// .collect::<String>() | |
32a655c1 SL |
714 | /// ``` |
715 | /// | |
716 | /// File 'main.rs': | |
717 | /// | |
041b39d2 | 718 | /// ```ignore (cannot-doctest-external-file-dependency) |
32a655c1 | 719 | /// fn main() { |
3b2f2976 XL |
720 | /// let my_string = include!("monkeys.in"); |
721 | /// assert_eq!("๐๐๐๐๐๐", my_string); | |
722 | /// println!("{}", my_string); | |
c34b1796 AL |
723 | /// } |
724 | /// ``` | |
32a655c1 | 725 | /// |
3b2f2976 XL |
726 | /// Compiling 'main.rs' and running the resulting binary will print |
727 | /// "๐๐๐๐๐๐". | |
92a42be0 | 728 | #[stable(feature = "rust1", since = "1.0.0")] |
c34b1796 | 729 | #[macro_export] |
0531ce1d XL |
730 | macro_rules! include { |
731 | ($file:expr) => ({ /* compiler built-in */ }); | |
732 | ($file:expr,) => ({ /* compiler built-in */ }); | |
733 | } | |
734 | ||
735 | /// Ensure that a boolean expression is `true` at runtime. | |
736 | /// | |
737 | /// This will invoke the [`panic!`] macro if the provided expression cannot be | |
738 | /// evaluated to `true` at runtime. | |
739 | /// | |
740 | /// # Uses | |
741 | /// | |
742 | /// Assertions are always checked in both debug and release builds, and cannot | |
743 | /// be disabled. See [`debug_assert!`] for assertions that are not enabled in | |
744 | /// release builds by default. | |
745 | /// | |
746 | /// Unsafe code relies on `assert!` to enforce run-time invariants that, if | |
747 | /// violated could lead to unsafety. | |
748 | /// | |
749 | /// Other use-cases of `assert!` include [testing] and enforcing run-time | |
750 | /// invariants in safe code (whose violation cannot result in unsafety). | |
751 | /// | |
752 | /// # Custom Messages | |
753 | /// | |
754 | /// This macro has a second form, where a custom panic message can | |
755 | /// be provided with or without arguments for formatting. See [`std::fmt`] | |
756 | /// for syntax for this form. | |
757 | /// | |
758 | /// [`panic!`]: macro.panic.html | |
759 | /// [`debug_assert!`]: macro.debug_assert.html | |
760 | /// [testing]: ../book/second-edition/ch11-01-writing-tests.html#checking-results-with-the-assert-macro | |
761 | /// [`std::fmt`]: ../std/fmt/index.html | |
762 | /// | |
763 | /// # Examples | |
764 | /// | |
765 | /// ``` | |
766 | /// // the panic message for these assertions is the stringified value of the | |
767 | /// // expression given. | |
768 | /// assert!(true); | |
769 | /// | |
770 | /// fn some_computation() -> bool { true } // a very simple function | |
771 | /// | |
772 | /// assert!(some_computation()); | |
773 | /// | |
774 | /// // assert with a custom message | |
775 | /// let x = true; | |
776 | /// assert!(x, "x wasn't true!"); | |
777 | /// | |
778 | /// let a = 3; let b = 27; | |
779 | /// assert!(a + b == 30, "a = {}, b = {}", a, b); | |
780 | /// ``` | |
781 | #[stable(feature = "rust1", since = "1.0.0")] | |
782 | #[macro_export] | |
783 | macro_rules! assert { | |
784 | ($cond:expr) => ({ /* compiler built-in */ }); | |
785 | ($cond:expr,) => ({ /* compiler built-in */ }); | |
786 | ($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ }); | |
787 | } | |
1a4d82fc | 788 | } |
abe05a73 | 789 | |
83c7162d | 790 | /// A macro for defining `#[cfg]` if-else statements. |
abe05a73 XL |
791 | /// |
792 | /// This is similar to the `if/elif` C preprocessor macro by allowing definition | |
793 | /// of a cascade of `#[cfg]` cases, emitting the implementation which matches | |
794 | /// first. | |
795 | /// | |
83c7162d | 796 | /// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code |
abe05a73 XL |
797 | /// without having to rewrite each clause multiple times. |
798 | macro_rules! cfg_if { | |
799 | ($( | |
800 | if #[cfg($($meta:meta),*)] { $($it:item)* } | |
801 | ) else * else { | |
802 | $($it2:item)* | |
803 | }) => { | |
804 | __cfg_if_items! { | |
805 | () ; | |
806 | $( ( ($($meta),*) ($($it)*) ), )* | |
807 | ( () ($($it2)*) ), | |
808 | } | |
809 | } | |
810 | } | |
811 | ||
812 | macro_rules! __cfg_if_items { | |
813 | (($($not:meta,)*) ; ) => {}; | |
814 | (($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => { | |
815 | __cfg_if_apply! { cfg(all(not(any($($not),*)), $($m,)*)), $($it)* } | |
816 | __cfg_if_items! { ($($not,)* $($m,)*) ; $($rest)* } | |
817 | } | |
818 | } | |
819 | ||
820 | macro_rules! __cfg_if_apply { | |
821 | ($m:meta, $($it:item)*) => { | |
822 | $(#[$m] $it)* | |
823 | } | |
824 | } |