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
17 /// The entry point for panic of Rust threads.
19 /// This macro is used to inject panic into a Rust thread, causing the thread to
20 /// panic entirely. Each thread's panic can be reaped as the `Box<Any>` type,
21 /// and the single-argument form of the `panic!` macro will be the value which
24 /// The multi-argument form of this macro panics with a string and has the
25 /// `format!` syntax for building a string.
27 /// # Current implementation
29 /// If the main thread panics it will terminate all your threads and end your
30 /// program with code `101`.
35 /// # #![allow(unreachable_code)]
37 /// panic!("this is a terrible mistake!");
38 /// panic!(4); // panic with the value of 4 to be collected elsewhere
39 /// panic!("this is a {} {message}", "fancy", message = "message");
42 #[stable(feature = "rust1", since = "1.0.0")]
43 #[allow_internal_unstable]
46 panic!("explicit panic")
49 $crate::rt::begin_panic_new($msg, {
50 // static requires less code at runtime, more constant data
51 static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(), column!());
55 ($fmt:expr, $($arg:tt)+) => ({
56 $crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+), {
57 // The leading _'s are to avoid dead code warnings if this is
58 // used inside a dead function. Just `#[allow(dead_code)]` is
59 // insufficient, since the user may have
60 // `#[forbid(dead_code)]` and which cannot be overridden.
61 static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(), column!());
67 /// Macro for printing to the standard output.
69 /// Equivalent to the `println!` macro except that a newline is not printed at
70 /// the end of the message.
72 /// Note that stdout is frequently line-buffered by default so it may be
73 /// necessary to use `io::stdout().flush()` to ensure the output is emitted
76 /// Use `print!` only for the primary output of your program. Use
77 /// `eprint!` instead to print error and progress messages.
81 /// Panics if writing to `io::stdout()` fails.
86 /// use std::io::{self, Write};
96 /// io::stdout().flush().unwrap();
98 /// print!("this string has a newline, why not choose println! instead?\n");
100 /// io::stdout().flush().unwrap();
103 #[stable(feature = "rust1", since = "1.0.0")]
104 #[allow_internal_unstable]
106 ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
109 /// Macro for printing to the standard output, with a newline. On all
110 /// platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
111 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
113 /// Use the `format!` syntax to write data to the standard output.
114 /// See `std::fmt` for more information.
116 /// Use `println!` only for the primary output of your program. Use
117 /// `eprintln!` instead to print error and progress messages.
121 /// Panics if writing to `io::stdout` fails.
126 /// println!(); // prints just a newline
127 /// println!("hello there!");
128 /// println!("format {} arguments", "some");
131 #[stable(feature = "rust1", since = "1.0.0")]
132 macro_rules! println {
133 () => (print!("\n"));
134 ($fmt:expr) => (print!(concat!($fmt, "\n")));
135 ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
138 /// Macro for printing to the standard error.
140 /// Equivalent to the `print!` macro, except that output goes to
141 /// `io::stderr` instead of `io::stdout`. See `print!` for
144 /// Use `eprint!` only for error and progress messages. Use `print!`
145 /// instead for the primary output of your program.
149 /// Panics if writing to `io::stderr` fails.
151 #[stable(feature = "eprint", since = "1.19.0")]
152 #[allow_internal_unstable]
153 macro_rules! eprint {
154 ($($arg:tt)*) => ($crate::io::_eprint(format_args!($($arg)*)));
157 /// Macro for printing to the standard error, with a newline.
159 /// Equivalent to the `println!` macro, except that output goes to
160 /// `io::stderr` instead of `io::stdout`. See `println!` for
163 /// Use `eprintln!` only for error and progress messages. Use `println!`
164 /// instead for the primary output of your program.
168 /// Panics if writing to `io::stderr` fails.
170 #[stable(feature = "eprint", since = "1.19.0")]
171 macro_rules! eprintln {
172 () => (eprint!("\n"));
173 ($fmt:expr) => (eprint!(concat!($fmt, "\n")));
174 ($fmt:expr, $($arg:tt)*) => (eprint!(concat!($fmt, "\n"), $($arg)*));
177 /// A macro to select an event from a number of receivers.
179 /// This macro is used to wait for the first event to occur on a number of
180 /// receivers. It places no restrictions on the types of receivers given to
181 /// this macro, this can be viewed as a heterogeneous select.
186 /// #![feature(mpsc_select)]
189 /// use std::sync::mpsc;
191 /// // two placeholder functions for now
192 /// fn long_running_thread() {}
193 /// fn calculate_the_answer() -> u32 { 42 }
195 /// let (tx1, rx1) = mpsc::channel();
196 /// let (tx2, rx2) = mpsc::channel();
198 /// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); });
199 /// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); });
202 /// _ = rx1.recv() => println!("the long running thread finished first"),
203 /// answer = rx2.recv() => {
204 /// println!("the answer was: {}", answer.unwrap());
207 /// # drop(rx1.recv());
208 /// # drop(rx2.recv());
211 /// For more information about select, see the `std::sync::mpsc::Select` structure.
213 #[unstable(feature = "mpsc_select", issue = "27800")]
214 macro_rules! select {
216 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
218 use $crate::sync::mpsc::Select;
219 let sel = Select::new();
220 $( let mut $rx = sel.handle(&$rx); )+
224 let ret = sel.wait();
225 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
231 macro_rules! assert_approx_eq {
232 ($a:expr, $b:expr) => ({
233 let (a, b) = (&$a, &$b);
234 assert!((*a - *b).abs() < 1.0e-6,
235 "{} is not approximately equal to {}", *a, *b);
239 /// Built-in macros to the compiler itself.
241 /// These macros do not have any corresponding definition with a `macro_rules!`
242 /// macro, but are documented here. Their implementations can be found hardcoded
243 /// into libsyntax itself.
247 /// Unconditionally causes compilation to fail with the given error message when encountered.
249 /// For more information, see the [RFC].
251 /// [RFC]: https://github.com/rust-lang/rfcs/blob/master/text/1695-add-error-macro.md
252 #[unstable(feature = "compile_error_macro", issue = "40872")]
254 macro_rules! compile_error { ($msg:expr) => ({ /* compiler built-in */ }) }
256 /// The core macro for formatted string creation & output.
258 /// This macro produces a value of type [`fmt::Arguments`]. This value can be
259 /// passed to the functions in [`std::fmt`] for performing useful functions.
260 /// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
261 /// proxied through this one.
263 /// For more information, see the documentation in [`std::fmt`].
265 /// [`fmt::Arguments`]: ../std/fmt/struct.Arguments.html
266 /// [`std::fmt`]: ../std/fmt/index.html
267 /// [`format!`]: ../std/macro.format.html
268 /// [`write!`]: ../std/macro.write.html
269 /// [`println!`]: ../std/macro.println.html
276 /// let s = fmt::format(format_args!("hello {}", "world"));
277 /// assert_eq!(s, format!("hello {}", "world"));
280 #[stable(feature = "rust1", since = "1.0.0")]
282 macro_rules! format_args { ($fmt:expr, $($args:tt)*) => ({
283 /* compiler built-in */
286 /// Inspect an environment variable at compile time.
288 /// This macro will expand to the value of the named environment variable at
289 /// compile time, yielding an expression of type `&'static str`.
291 /// If the environment variable is not defined, then a compilation error
292 /// will be emitted. To not emit a compile error, use the `option_env!`
298 /// let path: &'static str = env!("PATH");
299 /// println!("the $PATH variable at the time of compiling was: {}", path);
301 #[stable(feature = "rust1", since = "1.0.0")]
303 macro_rules! env { ($name:expr) => ({ /* compiler built-in */ }) }
305 /// Optionally inspect an environment variable at compile time.
307 /// If the named environment variable is present at compile time, this will
308 /// expand into an expression of type `Option<&'static str>` whose value is
309 /// `Some` of the value of the environment variable. If the environment
310 /// variable is not present, then this will expand to `None`.
312 /// A compile time error is never emitted when using this macro regardless
313 /// of whether the environment variable is present or not.
318 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
319 /// println!("the secret key might be: {:?}", key);
321 #[stable(feature = "rust1", since = "1.0.0")]
323 macro_rules! option_env { ($name:expr) => ({ /* compiler built-in */ }) }
325 /// Concatenate identifiers into one identifier.
327 /// This macro takes any number of comma-separated identifiers, and
328 /// concatenates them all into one, yielding an expression which is a new
329 /// identifier. Note that hygiene makes it such that this macro cannot
330 /// capture local variables. Also, as a general rule, macros are only
331 /// allowed in item, statement or expression position. That means while
332 /// you may use this macro for referring to existing variables, functions or
333 /// modules etc, you cannot define a new one with it.
338 /// #![feature(concat_idents)]
341 /// fn foobar() -> u32 { 23 }
343 /// let f = concat_idents!(foo, bar);
344 /// println!("{}", f());
346 /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
349 #[unstable(feature = "concat_idents_macro", issue = "29599")]
351 macro_rules! concat_idents {
352 ($($e:ident),*) => ({ /* compiler built-in */ })
355 /// Concatenates literals into a static string slice.
357 /// This macro takes any number of comma-separated literals, yielding an
358 /// expression of type `&'static str` which represents all of the literals
359 /// concatenated left-to-right.
361 /// Integer and floating point literals are stringified in order to be
367 /// let s = concat!("test", 10, 'b', true);
368 /// assert_eq!(s, "test10btrue");
370 #[stable(feature = "rust1", since = "1.0.0")]
372 macro_rules! concat { ($($e:expr),*) => ({ /* compiler built-in */ }) }
374 /// A macro which expands to the line number on which it was invoked.
376 /// The expanded expression has type `u32`, and the returned line is not
377 /// the invocation of the `line!()` macro itself, but rather the first macro
378 /// invocation leading up to the invocation of the `line!()` macro.
383 /// let current_line = line!();
384 /// println!("defined on line: {}", current_line);
386 #[stable(feature = "rust1", since = "1.0.0")]
388 macro_rules! line { () => ({ /* compiler built-in */ }) }
390 /// A macro which expands to the column number on which it was invoked.
392 /// The expanded expression has type `u32`, and the returned column is not
393 /// the invocation of the `column!()` macro itself, but rather the first macro
394 /// invocation leading up to the invocation of the `column!()` macro.
399 /// let current_col = column!();
400 /// println!("defined on column: {}", current_col);
402 #[stable(feature = "rust1", since = "1.0.0")]
404 macro_rules! column { () => ({ /* compiler built-in */ }) }
406 /// A macro which expands to the file name from which it was invoked.
408 /// The expanded expression has type `&'static str`, and the returned file
409 /// is not the invocation of the `file!()` macro itself, but rather the
410 /// first macro invocation leading up to the invocation of the `file!()`
416 /// let this_file = file!();
417 /// println!("defined in file: {}", this_file);
419 #[stable(feature = "rust1", since = "1.0.0")]
421 macro_rules! file { () => ({ /* compiler built-in */ }) }
423 /// A macro which stringifies its argument.
425 /// This macro will yield an expression of type `&'static str` which is the
426 /// stringification of all the tokens passed to the macro. No restrictions
427 /// are placed on the syntax of the macro invocation itself.
429 /// Note that the expanded results of the input tokens may change in the
430 /// future. You should be careful if you rely on the output.
435 /// let one_plus_one = stringify!(1 + 1);
436 /// assert_eq!(one_plus_one, "1 + 1");
438 #[stable(feature = "rust1", since = "1.0.0")]
440 macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
442 /// Includes a utf8-encoded file as a string.
444 /// The file is located relative to the current file. (similarly to how
445 /// modules are found)
447 /// This macro will yield an expression of type `&'static str` which is the
448 /// contents of the file.
452 /// ```ignore (cannot-doctest-external-file-dependency)
453 /// let secret_key = include_str!("secret-key.ascii");
455 #[stable(feature = "rust1", since = "1.0.0")]
457 macro_rules! include_str { ($file:expr) => ({ /* compiler built-in */ }) }
459 /// Includes a file as a reference to a byte array.
461 /// The file is located relative to the current file. (similarly to how
462 /// modules are found)
464 /// This macro will yield an expression of type `&'static [u8; N]` which is
465 /// the contents of the file.
469 /// ```ignore (cannot-doctest-external-file-dependency)
470 /// let secret_key = include_bytes!("secret-key.bin");
472 #[stable(feature = "rust1", since = "1.0.0")]
474 macro_rules! include_bytes { ($file:expr) => ({ /* compiler built-in */ }) }
476 /// Expands to a string that represents the current module path.
478 /// The current module path can be thought of as the hierarchy of modules
479 /// leading back up to the crate root. The first component of the path
480 /// returned is the name of the crate currently being compiled.
487 /// assert!(module_path!().ends_with("test"));
493 #[stable(feature = "rust1", since = "1.0.0")]
495 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
497 /// Boolean evaluation of configuration flags.
499 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
500 /// boolean expression evaluation of configuration flags. This frequently
501 /// leads to less duplicated code.
503 /// The syntax given to this macro is the same syntax as [the `cfg`
504 /// attribute](../book/first-edition/conditional-compilation.html).
509 /// let my_directory = if cfg!(windows) {
510 /// "windows-specific-directory"
515 #[stable(feature = "rust1", since = "1.0.0")]
517 macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
519 /// Parse a file as an expression or an item according to the context.
521 /// The file is located relative to the current file (similarly to how
522 /// modules are found).
524 /// Using this macro is often a bad idea, because if the file is
525 /// parsed as an expression, it is going to be placed in the
526 /// surrounding code unhygienically. This could result in variables
527 /// or functions being different from what the file expected if
528 /// there are variables or functions that have the same name in
529 /// the current file.
533 /// Assume there are two files in the same directory with the following
536 /// File 'my_str.in':
538 /// ```ignore (only-for-syntax-highlight)
544 /// ```ignore (cannot-doctest-external-file-dependency)
546 /// let my_str = include!("my_str.in");
547 /// println!("{}", my_str);
551 /// Compiling 'main.rs' and running the resulting binary will print "Hello
553 #[stable(feature = "rust1", since = "1.0.0")]
555 macro_rules! include { ($file:expr) => ({ /* compiler built-in */ }) }