1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
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.
11 //! Standard library macros
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
18 // This stability attribute is totally useless.
19 #[stable(feature = "rust1", since = "1.0.0")]
21 macro_rules! __rust_unstable_column {
27 /// The entry point for panic of Rust threads.
29 /// This macro is used to inject panic into a Rust thread, causing the thread to
30 /// panic entirely. Each thread's panic can be reaped as the `Box<Any>` type,
31 /// and the single-argument form of the `panic!` macro will be the value which
34 /// The multi-argument form of this macro panics with a string and has the
35 /// `format!` syntax for building a string.
37 /// # Current implementation
39 /// If the main thread panics it will terminate all your threads and end your
40 /// program with code `101`.
45 /// # #![allow(unreachable_code)]
47 /// panic!("this is a terrible mistake!");
48 /// panic!(4); // panic with the value of 4 to be collected elsewhere
49 /// panic!("this is a {} {message}", "fancy", message = "message");
52 #[stable(feature = "rust1", since = "1.0.0")]
53 #[allow_internal_unstable]
56 panic!("explicit panic")
59 $crate::rt::begin_panic($msg, {
60 // static requires less code at runtime, more constant data
61 static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(),
62 __rust_unstable_column!());
66 ($fmt:expr, $($arg:tt)+) => ({
67 $crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+), {
68 // The leading _'s are to avoid dead code warnings if this is
69 // used inside a dead function. Just `#[allow(dead_code)]` is
70 // insufficient, since the user may have
71 // `#[forbid(dead_code)]` and which cannot be overridden.
72 static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(),
73 __rust_unstable_column!());
79 /// Macro for printing to the standard output.
81 /// Equivalent to the `println!` macro except that a newline is not printed at
82 /// the end of the message.
84 /// Note that stdout is frequently line-buffered by default so it may be
85 /// necessary to use `io::stdout().flush()` to ensure the output is emitted
88 /// Use `print!` only for the primary output of your program. Use
89 /// `eprint!` instead to print error and progress messages.
93 /// Panics if writing to `io::stdout()` fails.
98 /// use std::io::{self, Write};
108 /// io::stdout().flush().unwrap();
110 /// print!("this string has a newline, why not choose println! instead?\n");
112 /// io::stdout().flush().unwrap();
115 #[stable(feature = "rust1", since = "1.0.0")]
116 #[allow_internal_unstable]
118 ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
121 /// Macro for printing to the standard output, with a newline. On all
122 /// platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
123 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
125 /// Use the `format!` syntax to write data to the standard output.
126 /// See `std::fmt` for more information.
128 /// Use `println!` only for the primary output of your program. Use
129 /// `eprintln!` instead to print error and progress messages.
133 /// Panics if writing to `io::stdout` fails.
138 /// println!(); // prints just a newline
139 /// println!("hello there!");
140 /// println!("format {} arguments", "some");
143 #[stable(feature = "rust1", since = "1.0.0")]
144 macro_rules! println {
145 () => (print!("\n"));
146 ($fmt:expr) => (print!(concat!($fmt, "\n")));
147 ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
150 /// Macro for printing to the standard error.
152 /// Equivalent to the `print!` macro, except that output goes to
153 /// `io::stderr` instead of `io::stdout`. See `print!` for
156 /// Use `eprint!` only for error and progress messages. Use `print!`
157 /// instead for the primary output of your program.
161 /// Panics if writing to `io::stderr` fails.
163 #[stable(feature = "eprint", since = "1.19.0")]
164 #[allow_internal_unstable]
165 macro_rules! eprint {
166 ($($arg:tt)*) => ($crate::io::_eprint(format_args!($($arg)*)));
169 /// Macro for printing to the standard error, with a newline.
171 /// Equivalent to the `println!` macro, except that output goes to
172 /// `io::stderr` instead of `io::stdout`. See `println!` for
175 /// Use `eprintln!` only for error and progress messages. Use `println!`
176 /// instead for the primary output of your program.
180 /// Panics if writing to `io::stderr` fails.
182 #[stable(feature = "eprint", since = "1.19.0")]
183 macro_rules! eprintln {
184 () => (eprint!("\n"));
185 ($fmt:expr) => (eprint!(concat!($fmt, "\n")));
186 ($fmt:expr, $($arg:tt)*) => (eprint!(concat!($fmt, "\n"), $($arg)*));
189 /// A macro to select an event from a number of receivers.
191 /// This macro is used to wait for the first event to occur on a number of
192 /// receivers. It places no restrictions on the types of receivers given to
193 /// this macro, this can be viewed as a heterogeneous select.
198 /// #![feature(mpsc_select)]
201 /// use std::sync::mpsc;
203 /// // two placeholder functions for now
204 /// fn long_running_thread() {}
205 /// fn calculate_the_answer() -> u32 { 42 }
207 /// let (tx1, rx1) = mpsc::channel();
208 /// let (tx2, rx2) = mpsc::channel();
210 /// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); });
211 /// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); });
214 /// _ = rx1.recv() => println!("the long running thread finished first"),
215 /// answer = rx2.recv() => {
216 /// println!("the answer was: {}", answer.unwrap());
219 /// # drop(rx1.recv());
220 /// # drop(rx2.recv());
223 /// For more information about select, see the `std::sync::mpsc::Select` structure.
225 #[unstable(feature = "mpsc_select", issue = "27800")]
226 macro_rules! select {
228 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
230 use $crate::sync::mpsc::Select;
231 let sel = Select::new();
232 $( let mut $rx = sel.handle(&$rx); )+
236 let ret = sel.wait();
237 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
243 macro_rules! assert_approx_eq {
244 ($a:expr, $b:expr) => ({
245 let (a, b) = (&$a, &$b);
246 assert!((*a - *b).abs() < 1.0e-6,
247 "{} is not approximately equal to {}", *a, *b);
251 /// Built-in macros to the compiler itself.
253 /// These macros do not have any corresponding definition with a `macro_rules!`
254 /// macro, but are documented here. Their implementations can be found hardcoded
255 /// into libsyntax itself.
259 /// Unconditionally causes compilation to fail with the given error message when encountered.
261 /// For more information, see the [RFC].
263 /// [RFC]: https://github.com/rust-lang/rfcs/blob/master/text/1695-add-error-macro.md
264 #[stable(feature = "compile_error_macro", since = "1.20.0")]
266 macro_rules! compile_error { ($msg:expr) => ({ /* compiler built-in */ }) }
268 /// The core macro for formatted string creation & output.
270 /// This macro produces a value of type [`fmt::Arguments`]. This value can be
271 /// passed to the functions in [`std::fmt`] for performing useful functions.
272 /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
273 /// proxied through this one.
275 /// For more information, see the documentation in [`std::fmt`].
277 /// [`fmt::Arguments`]: ../std/fmt/struct.Arguments.html
278 /// [`std::fmt`]: ../std/fmt/index.html
279 /// [`format!`]: ../std/macro.format.html
280 /// [`write!`]: ../std/macro.write.html
281 /// [`println!`]: ../std/macro.println.html
288 /// let s = fmt::format(format_args!("hello {}", "world"));
289 /// assert_eq!(s, format!("hello {}", "world"));
292 #[stable(feature = "rust1", since = "1.0.0")]
294 macro_rules! format_args { ($fmt:expr, $($args:tt)*) => ({
295 /* compiler built-in */
298 /// Inspect an environment variable at compile time.
300 /// This macro will expand to the value of the named environment variable at
301 /// compile time, yielding an expression of type `&'static str`.
303 /// If the environment variable is not defined, then a compilation error
304 /// will be emitted. To not emit a compile error, use the `option_env!`
310 /// let path: &'static str = env!("PATH");
311 /// println!("the $PATH variable at the time of compiling was: {}", path);
313 #[stable(feature = "rust1", since = "1.0.0")]
315 macro_rules! env { ($name:expr) => ({ /* compiler built-in */ }) }
317 /// Optionally inspect an environment variable at compile time.
319 /// If the named environment variable is present at compile time, this will
320 /// expand into an expression of type `Option<&'static str>` whose value is
321 /// `Some` of the value of the environment variable. If the environment
322 /// variable is not present, then this will expand to `None`.
324 /// A compile time error is never emitted when using this macro regardless
325 /// of whether the environment variable is present or not.
330 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
331 /// println!("the secret key might be: {:?}", key);
333 #[stable(feature = "rust1", since = "1.0.0")]
335 macro_rules! option_env { ($name:expr) => ({ /* compiler built-in */ }) }
337 /// Concatenate identifiers into one identifier.
339 /// This macro takes any number of comma-separated identifiers, and
340 /// concatenates them all into one, yielding an expression which is a new
341 /// identifier. Note that hygiene makes it such that this macro cannot
342 /// capture local variables. Also, as a general rule, macros are only
343 /// allowed in item, statement or expression position. That means while
344 /// you may use this macro for referring to existing variables, functions or
345 /// modules etc, you cannot define a new one with it.
350 /// #![feature(concat_idents)]
353 /// fn foobar() -> u32 { 23 }
355 /// let f = concat_idents!(foo, bar);
356 /// println!("{}", f());
358 /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
361 #[unstable(feature = "concat_idents_macro", issue = "29599")]
363 macro_rules! concat_idents {
364 ($($e:ident),*) => ({ /* compiler built-in */ })
367 /// Concatenates literals into a static string slice.
369 /// This macro takes any number of comma-separated literals, yielding an
370 /// expression of type `&'static str` which represents all of the literals
371 /// concatenated left-to-right.
373 /// Integer and floating point literals are stringified in order to be
379 /// let s = concat!("test", 10, 'b', true);
380 /// assert_eq!(s, "test10btrue");
382 #[stable(feature = "rust1", since = "1.0.0")]
384 macro_rules! concat { ($($e:expr),*) => ({ /* compiler built-in */ }) }
386 /// A macro which expands to the line number on which it was invoked.
388 /// The expanded expression has type `u32`, and the returned line is not
389 /// the invocation of the `line!()` macro itself, but rather the first macro
390 /// invocation leading up to the invocation of the `line!()` macro.
395 /// let current_line = line!();
396 /// println!("defined on line: {}", current_line);
398 #[stable(feature = "rust1", since = "1.0.0")]
400 macro_rules! line { () => ({ /* compiler built-in */ }) }
402 /// A macro which expands to the column number on which it was invoked.
404 /// The expanded expression has type `u32`, and the returned column is not
405 /// the invocation of the `column!()` macro itself, but rather the first macro
406 /// invocation leading up to the invocation of the `column!()` macro.
411 /// let current_col = column!();
412 /// println!("defined on column: {}", current_col);
414 #[stable(feature = "rust1", since = "1.0.0")]
416 macro_rules! column { () => ({ /* compiler built-in */ }) }
418 /// A macro which expands to the file name from which it was invoked.
420 /// The expanded expression has type `&'static str`, and the returned file
421 /// is not the invocation of the `file!()` macro itself, but rather the
422 /// first macro invocation leading up to the invocation of the `file!()`
428 /// let this_file = file!();
429 /// println!("defined in file: {}", this_file);
431 #[stable(feature = "rust1", since = "1.0.0")]
433 macro_rules! file { () => ({ /* compiler built-in */ }) }
435 /// A macro which stringifies its argument.
437 /// This macro will yield an expression of type `&'static str` which is the
438 /// stringification of all the tokens passed to the macro. No restrictions
439 /// are placed on the syntax of the macro invocation itself.
441 /// Note that the expanded results of the input tokens may change in the
442 /// future. You should be careful if you rely on the output.
447 /// let one_plus_one = stringify!(1 + 1);
448 /// assert_eq!(one_plus_one, "1 + 1");
450 #[stable(feature = "rust1", since = "1.0.0")]
452 macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
454 /// Includes a utf8-encoded file as a string.
456 /// The file is located relative to the current file. (similarly to how
457 /// modules are found)
459 /// This macro will yield an expression of type `&'static str` which is the
460 /// contents of the file.
464 /// ```ignore (cannot-doctest-external-file-dependency)
465 /// let secret_key = include_str!("secret-key.ascii");
467 #[stable(feature = "rust1", since = "1.0.0")]
469 macro_rules! include_str { ($file:expr) => ({ /* compiler built-in */ }) }
471 /// Includes a file as a reference to a byte array.
473 /// The file is located relative to the current file. (similarly to how
474 /// modules are found)
476 /// This macro will yield an expression of type `&'static [u8; N]` which is
477 /// the contents of the file.
481 /// ```ignore (cannot-doctest-external-file-dependency)
482 /// let secret_key = include_bytes!("secret-key.bin");
484 #[stable(feature = "rust1", since = "1.0.0")]
486 macro_rules! include_bytes { ($file:expr) => ({ /* compiler built-in */ }) }
488 /// Expands to a string that represents the current module path.
490 /// The current module path can be thought of as the hierarchy of modules
491 /// leading back up to the crate root. The first component of the path
492 /// returned is the name of the crate currently being compiled.
499 /// assert!(module_path!().ends_with("test"));
505 #[stable(feature = "rust1", since = "1.0.0")]
507 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
509 /// Boolean evaluation of configuration flags.
511 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
512 /// boolean expression evaluation of configuration flags. This frequently
513 /// leads to less duplicated code.
515 /// The syntax given to this macro is the same syntax as [the `cfg`
516 /// attribute](../book/first-edition/conditional-compilation.html).
521 /// let my_directory = if cfg!(windows) {
522 /// "windows-specific-directory"
527 #[stable(feature = "rust1", since = "1.0.0")]
529 macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
531 /// Parse a file as an expression or an item according to the context.
533 /// The file is located relative to the current file (similarly to how
534 /// modules are found).
536 /// Using this macro is often a bad idea, because if the file is
537 /// parsed as an expression, it is going to be placed in the
538 /// surrounding code unhygienically. This could result in variables
539 /// or functions being different from what the file expected if
540 /// there are variables or functions that have the same name in
541 /// the current file.
545 /// Assume there are two files in the same directory with the following
548 /// File 'monkeys.in':
550 /// ```ignore (only-for-syntax-highlight)
551 /// ['🙈', '🙊', '🙉']
555 /// .collect::<String>()
560 /// ```ignore (cannot-doctest-external-file-dependency)
562 /// let my_string = include!("monkeys.in");
563 /// assert_eq!("🙈🙊🙉🙈🙊🙉", my_string);
564 /// println!("{}", my_string);
568 /// Compiling 'main.rs' and running the resulting binary will print
569 /// "🙈🙊🙉🙈🙊🙉".
570 #[stable(feature = "rust1", since = "1.0.0")]
572 macro_rules! include { ($file:expr) => ({ /* compiler built-in */ }) }