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 /// unwind and panic entirely. Each thread's panic can be reaped as the
21 /// `Box<Any>` type, and the single-argument form of the `panic!` macro will be
22 /// the value which is transmitted.
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 $crate::rt::begin_unwind($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 $crate::rt::begin_unwind_fmt(format_args!($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
71 #[stable(feature = "rust1", since = "1.0.0")]
72 #[allow_internal_unstable]
74 ($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
77 /// Macro for printing to the standard output.
79 /// Use the `format!` syntax to write data to the standard output.
80 /// See `std::fmt` for more information.
85 /// println!("hello there!");
86 /// println!("format {} arguments", "some");
89 #[stable(feature = "rust1", since = "1.0.0")]
90 macro_rules! println {
91 ($fmt:expr) => (print!(concat!($fmt, "\n")));
92 ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
95 /// Helper macro for unwrapping `Result` values while returning early with an
96 /// error if the value of the expression is `Err`. Can only be used in
97 /// functions that return `Result` because of the early return of `Err` that
104 /// use std::fs::File;
105 /// use std::io::prelude::*;
107 /// fn write_to_file_using_try() -> Result<(), io::Error> {
108 /// let mut file = try!(File::create("my_best_friends.txt"));
109 /// try!(file.write_all(b"This is a list of my best friends."));
110 /// println!("I wrote to the file");
113 /// // This is equivalent to:
114 /// fn write_to_file_using_match() -> Result<(), io::Error> {
115 /// let mut file = try!(File::create("my_best_friends.txt"));
116 /// match file.write_all(b"This is a list of my best friends.") {
118 /// Err(e) => return Err(e),
120 /// println!("I wrote to the file");
125 #[stable(feature = "rust1", since = "1.0.0")]
127 ($expr:expr) => (match $expr {
128 $crate::result::Result::Ok(val) => val,
129 $crate::result::Result::Err(err) => {
130 return $crate::result::Result::Err($crate::convert::From::from(err))
135 /// A macro to select an event from a number of receivers.
137 /// This macro is used to wait for the first event to occur on a number of
138 /// receivers. It places no restrictions on the types of receivers given to
139 /// this macro, this can be viewed as a heterogeneous select.
144 /// #![feature(mpsc_select)]
147 /// use std::sync::mpsc;
149 /// // two placeholder functions for now
150 /// fn long_running_thread() {}
151 /// fn calculate_the_answer() -> u32 { 42 }
153 /// let (tx1, rx1) = mpsc::channel();
154 /// let (tx2, rx2) = mpsc::channel();
156 /// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); });
157 /// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); });
160 /// _ = rx1.recv() => println!("the long running thread finished first"),
161 /// answer = rx2.recv() => {
162 /// println!("the answer was: {}", answer.unwrap());
165 /// # drop(rx1.recv());
166 /// # drop(rx2.recv());
169 /// For more information about select, see the `std::sync::mpsc::Select` structure.
171 #[unstable(feature = "mpsc_select")]
172 macro_rules! select {
174 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
176 use $crate::sync::mpsc::Select;
177 let sel = Select::new();
178 $( let mut $rx = sel.handle(&$rx); )+
182 let ret = sel.wait();
183 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
188 // When testing the standard library, we link to the liblog crate to get the
189 // logging macros. In doing so, the liblog crate was linked against the real
190 // version of libstd, and uses a different std::fmt module than the test crate
191 // uses. To get around this difference, we redefine the log!() macro here to be
192 // just a dumb version of what it should be.
195 ($lvl:expr, $($args:tt)*) => (
196 if log_enabled!($lvl) { println!($($args)*) }
200 /// Built-in macros to the compiler itself.
202 /// These macros do not have any corresponding definition with a `macro_rules!`
203 /// macro, but are documented here. Their implementations can be found hardcoded
204 /// into libsyntax itself.
207 /// The core macro for formatted string creation & output.
209 /// This macro produces a value of type `fmt::Arguments`. This value can be
210 /// passed to the functions in `std::fmt` for performing useful functions.
211 /// All other formatting macros (`format!`, `write!`, `println!`, etc) are
212 /// proxied through this one.
214 /// For more information, see the documentation in `std::fmt`.
221 /// let s = fmt::format(format_args!("hello {}", "world"));
222 /// assert_eq!(s, format!("hello {}", "world"));
226 macro_rules! format_args { ($fmt:expr, $($args:tt)*) => ({
227 /* compiler built-in */
230 /// Inspect an environment variable at compile time.
232 /// This macro will expand to the value of the named environment variable at
233 /// compile time, yielding an expression of type `&'static str`.
235 /// If the environment variable is not defined, then a compilation error
236 /// will be emitted. To not emit a compile error, use the `option_env!`
242 /// let path: &'static str = env!("PATH");
243 /// println!("the $PATH variable at the time of compiling was: {}", path);
246 macro_rules! env { ($name:expr) => ({ /* compiler built-in */ }) }
248 /// Optionally inspect an environment variable at compile time.
250 /// If the named environment variable is present at compile time, this will
251 /// expand into an expression of type `Option<&'static str>` whose value is
252 /// `Some` of the value of the environment variable. If the environment
253 /// variable is not present, then this will expand to `None`.
255 /// A compile time error is never emitted when using this macro regardless
256 /// of whether the environment variable is present or not.
261 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
262 /// println!("the secret key might be: {:?}", key);
265 macro_rules! option_env { ($name:expr) => ({ /* compiler built-in */ }) }
267 /// Concatenate identifiers into one identifier.
269 /// This macro takes any number of comma-separated identifiers, and
270 /// concatenates them all into one, yielding an expression which is a new
271 /// identifier. Note that hygiene makes it such that this macro cannot
272 /// capture local variables, and macros are only allowed in item,
273 /// statement or expression position, meaning this macro may be difficult to
274 /// use in some situations.
279 /// #![feature(concat_idents)]
282 /// fn foobar() -> u32 { 23 }
284 /// let f = concat_idents!(foo, bar);
285 /// println!("{}", f());
289 macro_rules! concat_idents {
290 ($($e:ident),*) => ({ /* compiler built-in */ })
293 /// Concatenates literals into a static string slice.
295 /// This macro takes any number of comma-separated literals, yielding an
296 /// expression of type `&'static str` which represents all of the literals
297 /// concatenated left-to-right.
299 /// Integer and floating point literals are stringified in order to be
305 /// let s = concat!("test", 10, 'b', true);
306 /// assert_eq!(s, "test10btrue");
309 macro_rules! concat { ($($e:expr),*) => ({ /* compiler built-in */ }) }
311 /// A macro which expands to the line number on which it was invoked.
313 /// The expanded expression has type `u32`, and the returned line is not
314 /// the invocation of the `line!()` macro itself, but rather the first macro
315 /// invocation leading up to the invocation of the `line!()` macro.
320 /// let current_line = line!();
321 /// println!("defined on line: {}", current_line);
324 macro_rules! line { () => ({ /* compiler built-in */ }) }
326 /// A macro which expands to the column number on which it was invoked.
328 /// The expanded expression has type `u32`, and the returned column is not
329 /// the invocation of the `column!()` macro itself, but rather the first macro
330 /// invocation leading up to the invocation of the `column!()` macro.
335 /// let current_col = column!();
336 /// println!("defined on column: {}", current_col);
339 macro_rules! column { () => ({ /* compiler built-in */ }) }
341 /// A macro which expands to the file name from which it was invoked.
343 /// The expanded expression has type `&'static str`, and the returned file
344 /// is not the invocation of the `file!()` macro itself, but rather the
345 /// first macro invocation leading up to the invocation of the `file!()`
351 /// let this_file = file!();
352 /// println!("defined in file: {}", this_file);
355 macro_rules! file { () => ({ /* compiler built-in */ }) }
357 /// A macro which stringifies its argument.
359 /// This macro will yield an expression of type `&'static str` which is the
360 /// stringification of all the tokens passed to the macro. No restrictions
361 /// are placed on the syntax of the macro invocation itself.
366 /// let one_plus_one = stringify!(1 + 1);
367 /// assert_eq!(one_plus_one, "1 + 1");
370 macro_rules! stringify { ($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");
384 macro_rules! include_str { ($file:expr) => ({ /* compiler built-in */ }) }
386 /// Includes a file as a byte slice.
388 /// This macro will yield an expression of type `&'static [u8]` which is
389 /// the contents of the filename specified. The file is located relative to
390 /// the current file (similarly to how modules are found),
395 /// let secret_key = include_bytes!("secret-key.bin");
398 macro_rules! include_bytes { ($file:expr) => ({ /* compiler built-in */ }) }
400 /// Expands to a string that represents the current module path.
402 /// The current module path can be thought of as the hierarchy of modules
403 /// leading back up to the crate root. The first component of the path
404 /// returned is the name of the crate currently being compiled.
411 /// assert!(module_path!().ends_with("test"));
418 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
420 /// Boolean evaluation of configuration flags.
422 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
423 /// boolean expression evaluation of configuration flags. This frequently
424 /// leads to less duplicated code.
426 /// The syntax given to this macro is the same syntax as the `cfg`
432 /// let my_directory = if cfg!(windows) {
433 /// "windows-specific-directory"
439 macro_rules! cfg { ($cfg:tt) => ({ /* compiler built-in */ }) }
441 /// Parse the current given file as an expression.
443 /// This is generally a bad idea, because it's going to behave unhygienically.
449 /// include!("/path/to/a/file")
453 macro_rules! include { ($cfg:tt) => ({ /* compiler built-in */ }) }