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.
30 /// # #![allow(unreachable_code)]
32 /// panic!("this is a terrible mistake!");
33 /// panic!(4); // panic with the value of 4 to be collected elsewhere
34 /// panic!("this is a {} {message}", "fancy", message = "message");
37 #[stable(feature = "rust1", since = "1.0.0")]
38 #[allow_internal_unstable]
41 panic!("explicit panic")
44 $crate::rt::begin_panic($msg, {
45 // static requires less code at runtime, more constant data
46 static _FILE_LINE: (&'static str, u32) = (file!(), line!());
50 ($fmt:expr, $($arg:tt)+) => ({
51 $crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+), {
52 // The leading _'s are to avoid dead code warnings if this is
53 // used inside a dead function. Just `#[allow(dead_code)]` is
54 // insufficient, since the user may have
55 // `#[forbid(dead_code)]` and which cannot be overridden.
56 static _FILE_LINE: (&'static str, u32) = (file!(), line!());
62 /// Macro for printing to the standard output.
64 /// Equivalent to the `println!` macro except that a newline is not printed at
65 /// the end of the message.
67 /// Note that stdout is frequently line-buffered by default so it may be
68 /// necessary to use `io::stdout().flush()` to ensure the output is emitted
73 /// Panics if writing to `io::stdout()` fails.
78 /// use std::io::{self, Write};
88 /// io::stdout().flush().unwrap();
90 /// print!("this string has a newline, why not choose println! instead?\n");
92 /// io::stdout().flush().unwrap();
95 #[stable(feature = "rust1", since = "1.0.0")]
96 #[allow_internal_unstable]
98 ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
101 /// Macro for printing to the standard output, with a newline.
103 /// Use the `format!` syntax to write data to the standard output.
104 /// See `std::fmt` for more information.
108 /// Panics if writing to `io::stdout()` fails.
113 /// println!("hello there!");
114 /// println!("format {} arguments", "some");
117 #[stable(feature = "rust1", since = "1.0.0")]
118 macro_rules! println {
119 ($fmt:expr) => (print!(concat!($fmt, "\n")));
120 ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
123 /// A macro to select an event from a number of receivers.
125 /// This macro is used to wait for the first event to occur on a number of
126 /// receivers. It places no restrictions on the types of receivers given to
127 /// this macro, this can be viewed as a heterogeneous select.
132 /// #![feature(mpsc_select)]
135 /// use std::sync::mpsc;
137 /// // two placeholder functions for now
138 /// fn long_running_thread() {}
139 /// fn calculate_the_answer() -> u32 { 42 }
141 /// let (tx1, rx1) = mpsc::channel();
142 /// let (tx2, rx2) = mpsc::channel();
144 /// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); });
145 /// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); });
148 /// _ = rx1.recv() => println!("the long running thread finished first"),
149 /// answer = rx2.recv() => {
150 /// println!("the answer was: {}", answer.unwrap());
153 /// # drop(rx1.recv());
154 /// # drop(rx2.recv());
157 /// For more information about select, see the `std::sync::mpsc::Select` structure.
159 #[unstable(feature = "mpsc_select", issue = "27800")]
160 macro_rules! select {
162 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
164 use $crate::sync::mpsc::Select;
165 let sel = Select::new();
166 $( let mut $rx = sel.handle(&$rx); )+
170 let ret = sel.wait();
171 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
177 macro_rules! assert_approx_eq {
178 ($a:expr, $b:expr) => ({
179 let (a, b) = (&$a, &$b);
180 assert!((*a - *b).abs() < 1.0e-6,
181 "{} is not approximately equal to {}", *a, *b);
185 /// Built-in macros to the compiler itself.
187 /// These macros do not have any corresponding definition with a `macro_rules!`
188 /// macro, but are documented here. Their implementations can be found hardcoded
189 /// into libsyntax itself.
192 /// The core macro for formatted string creation & output.
194 /// This macro produces a value of type `fmt::Arguments`. This value can be
195 /// passed to the functions in `std::fmt` for performing useful functions.
196 /// All other formatting macros (`format!`, `write!`, `println!`, etc) are
197 /// proxied through this one.
199 /// For more information, see the documentation in `std::fmt`.
206 /// let s = fmt::format(format_args!("hello {}", "world"));
207 /// assert_eq!(s, format!("hello {}", "world"));
210 #[stable(feature = "rust1", since = "1.0.0")]
212 macro_rules! format_args { ($fmt:expr, $($args:tt)*) => ({
213 /* compiler built-in */
216 /// Inspect an environment variable at compile time.
218 /// This macro will expand to the value of the named environment variable at
219 /// compile time, yielding an expression of type `&'static str`.
221 /// If the environment variable is not defined, then a compilation error
222 /// will be emitted. To not emit a compile error, use the `option_env!`
228 /// let path: &'static str = env!("PATH");
229 /// println!("the $PATH variable at the time of compiling was: {}", path);
231 #[stable(feature = "rust1", since = "1.0.0")]
233 macro_rules! env { ($name:expr) => ({ /* compiler built-in */ }) }
235 /// Optionally inspect an environment variable at compile time.
237 /// If the named environment variable is present at compile time, this will
238 /// expand into an expression of type `Option<&'static str>` whose value is
239 /// `Some` of the value of the environment variable. If the environment
240 /// variable is not present, then this will expand to `None`.
242 /// A compile time error is never emitted when using this macro regardless
243 /// of whether the environment variable is present or not.
248 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
249 /// println!("the secret key might be: {:?}", key);
251 #[stable(feature = "rust1", since = "1.0.0")]
253 macro_rules! option_env { ($name:expr) => ({ /* compiler built-in */ }) }
255 /// Concatenate identifiers into one identifier.
257 /// This macro takes any number of comma-separated identifiers, and
258 /// concatenates them all into one, yielding an expression which is a new
259 /// identifier. Note that hygiene makes it such that this macro cannot
260 /// capture local variables. Also, as a general rule, macros are only
261 /// allowed in item, statement or expression position. That means while
262 /// you may use this macro for referring to existing variables, functions or
263 /// modules etc, you cannot define a new one with it.
268 /// #![feature(concat_idents)]
271 /// fn foobar() -> u32 { 23 }
273 /// let f = concat_idents!(foo, bar);
274 /// println!("{}", f());
276 /// // fn concat_idents!(new, fun, name) { } // not usable in this way!
279 #[unstable(feature = "concat_idents", issue = "29599")]
281 macro_rules! concat_idents {
282 ($($e:ident),*) => ({ /* compiler built-in */ })
285 /// Concatenates literals into a static string slice.
287 /// This macro takes any number of comma-separated literals, yielding an
288 /// expression of type `&'static str` which represents all of the literals
289 /// concatenated left-to-right.
291 /// Integer and floating point literals are stringified in order to be
297 /// let s = concat!("test", 10, 'b', true);
298 /// assert_eq!(s, "test10btrue");
300 #[stable(feature = "rust1", since = "1.0.0")]
302 macro_rules! concat { ($($e:expr),*) => ({ /* compiler built-in */ }) }
304 /// A macro which expands to the line number on which it was invoked.
306 /// The expanded expression has type `u32`, and the returned line is not
307 /// the invocation of the `line!()` macro itself, but rather the first macro
308 /// invocation leading up to the invocation of the `line!()` macro.
313 /// let current_line = line!();
314 /// println!("defined on line: {}", current_line);
316 #[stable(feature = "rust1", since = "1.0.0")]
318 macro_rules! line { () => ({ /* compiler built-in */ }) }
320 /// A macro which expands to the column number on which it was invoked.
322 /// The expanded expression has type `u32`, and the returned column is not
323 /// the invocation of the `column!()` macro itself, but rather the first macro
324 /// invocation leading up to the invocation of the `column!()` macro.
329 /// let current_col = column!();
330 /// println!("defined on column: {}", current_col);
332 #[stable(feature = "rust1", since = "1.0.0")]
334 macro_rules! column { () => ({ /* compiler built-in */ }) }
336 /// A macro which expands to the file name from which it was invoked.
338 /// The expanded expression has type `&'static str`, and the returned file
339 /// is not the invocation of the `file!()` macro itself, but rather the
340 /// first macro invocation leading up to the invocation of the `file!()`
346 /// let this_file = file!();
347 /// println!("defined in file: {}", this_file);
349 #[stable(feature = "rust1", since = "1.0.0")]
351 macro_rules! file { () => ({ /* compiler built-in */ }) }
353 /// A macro which stringifies its argument.
355 /// This macro will yield an expression of type `&'static str` which is the
356 /// stringification of all the tokens passed to the macro. No restrictions
357 /// are placed on the syntax of the macro invocation itself.
359 /// Note that the expanded results of the input tokens may change in the
360 /// future. You should be careful if you rely on the output.
365 /// let one_plus_one = stringify!(1 + 1);
366 /// assert_eq!(one_plus_one, "1 + 1");
368 #[stable(feature = "rust1", since = "1.0.0")]
370 macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
372 /// Includes a utf8-encoded file as a string.
374 /// This macro will yield an expression of type `&'static str` which is the
375 /// contents of the filename specified. The file is located relative to the
376 /// current file (similarly to how modules are found),
381 /// let secret_key = include_str!("secret-key.ascii");
383 #[stable(feature = "rust1", since = "1.0.0")]
385 macro_rules! include_str { ($file:expr) => ({ /* compiler built-in */ }) }
387 /// Includes a file as a reference to a byte array.
389 /// This macro will yield an expression of type `&'static [u8; N]` which is
390 /// the contents of the filename specified. The file is located relative to
391 /// the current file (similarly to how modules are found),
396 /// let secret_key = include_bytes!("secret-key.bin");
398 #[stable(feature = "rust1", since = "1.0.0")]
400 macro_rules! include_bytes { ($file:expr) => ({ /* compiler built-in */ }) }
402 /// Expands to a string that represents the current module path.
404 /// The current module path can be thought of as the hierarchy of modules
405 /// leading back up to the crate root. The first component of the path
406 /// returned is the name of the crate currently being compiled.
413 /// assert!(module_path!().ends_with("test"));
419 #[stable(feature = "rust1", since = "1.0.0")]
421 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
423 /// Boolean evaluation of configuration flags.
425 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
426 /// boolean expression evaluation of configuration flags. This frequently
427 /// leads to less duplicated code.
429 /// The syntax given to this macro is the same syntax as [the `cfg`
430 /// attribute](../reference.html#conditional-compilation).
435 /// let my_directory = if cfg!(windows) {
436 /// "windows-specific-directory"
441 #[stable(feature = "rust1", since = "1.0.0")]
443 macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
445 /// Parse the current given file as an expression.
447 /// This is generally a bad idea, because it's going to behave unhygienically.
453 /// include!("/path/to/a/file")
456 #[stable(feature = "rust1", since = "1.0.0")]
458 macro_rules! include { ($file:expr) => ({ /* compiler built-in */ }) }