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
20 /// The entry point for panic of Rust tasks.
22 /// This macro is used to inject panic into a Rust task, causing the task to
23 /// unwind and panic entirely. Each task's panic can be reaped as the
24 /// `Box<Any>` type, and the single-argument form of the `panic!` macro will be
25 /// the value which is transmitted.
27 /// The multi-argument form of this macro panics with a string and has the
28 /// `format!` syntax for building a string.
33 /// # #![allow(unreachable_code)]
35 /// panic!("this is a terrible mistake!");
36 /// panic!(4i); // panic with the value of 4 to be collected elsewhere
37 /// panic!("this is a {} {message}", "fancy", message = "message");
42 panic!("explicit panic")
45 // static requires less code at runtime, more constant data
46 static _FILE_LINE: (&'static str, uint) = (file!(), line!());
47 ::std::rt::begin_unwind($msg, &_FILE_LINE)
49 ($fmt:expr, $($arg:tt)*) => ({
50 // a closure can't have return type !, so we need a full
51 // function to pass to format_args!, *and* we need the
52 // file and line numbers right here; so an inner bare fn
53 // is our only choice.
55 // LLVM doesn't tend to inline this, presumably because begin_unwind_fmt
56 // is #[cold] and #[inline(never)] and because this is flagged as cold
57 // as returning !. We really do want this to be inlined, however,
58 // because it's just a tiny wrapper. Small wins (156K to 149K in size)
59 // were seen when forcing this to be inlined, and that number just goes
60 // up with the number of calls to panic!()
62 // The leading _'s are to avoid dead code warnings if this is
63 // used inside a dead function. Just `#[allow(dead_code)]` is
64 // insufficient, since the user may have
65 // `#[forbid(dead_code)]` and which cannot be overridden.
67 fn _run_fmt(fmt: &::std::fmt::Arguments) -> ! {
68 static _FILE_LINE: (&'static str, uint) = (file!(), line!());
69 ::std::rt::begin_unwind_fmt(fmt, &_FILE_LINE)
71 format_args!(_run_fmt, $fmt, $($arg)*)
75 /// Ensure that a boolean expression is `true` at runtime.
77 /// This will invoke the `panic!` macro if the provided expression cannot be
78 /// evaluated to `true` at runtime.
83 /// // the panic message for these assertions is the stringified value of the
84 /// // expression given.
86 /// # fn some_computation() -> bool { true }
87 /// assert!(some_computation());
89 /// // assert with a custom message
91 /// assert!(x, "x wasn't true!");
92 /// # let a = 3i; let b = 27i;
93 /// assert!(a + b == 30, "a = {}, b = {}", a, b);
99 panic!(concat!("assertion failed: ", stringify!($cond)))
102 ($cond:expr, $($arg:expr),+) => (
109 /// Asserts that two expressions are equal to each other, testing equality in
112 /// On panic, this macro will print the values of the expressions.
119 /// assert_eq!(a, b);
122 macro_rules! assert_eq(
123 ($given:expr , $expected:expr) => ({
124 match (&($given), &($expected)) {
125 (given_val, expected_val) => {
126 // check both directions of equality....
127 if !((*given_val == *expected_val) &&
128 (*expected_val == *given_val)) {
129 panic!("assertion failed: `(left == right) && (right == left)` \
130 (left: `{}`, right: `{}`)", *given_val, *expected_val)
137 /// Ensure that a boolean expression is `true` at runtime.
139 /// This will invoke the `panic!` macro if the provided expression cannot be
140 /// evaluated to `true` at runtime.
142 /// Unlike `assert!`, `debug_assert!` statements can be disabled by passing
143 /// `--cfg ndebug` to the compiler. This makes `debug_assert!` useful for
144 /// checks that are too expensive to be present in a release build but may be
145 /// helpful during development.
150 /// // the panic message for these assertions is the stringified value of the
151 /// // expression given.
152 /// debug_assert!(true);
153 /// # fn some_expensive_computation() -> bool { true }
154 /// debug_assert!(some_expensive_computation());
156 /// // assert with a custom message
158 /// debug_assert!(x, "x wasn't true!");
159 /// # let a = 3i; let b = 27i;
160 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
163 macro_rules! debug_assert(
164 ($($arg:tt)*) => (if cfg!(not(ndebug)) { assert!($($arg)*); })
167 /// Asserts that two expressions are equal to each other, testing equality in
170 /// On panic, this macro will print the values of the expressions.
172 /// Unlike `assert_eq!`, `debug_assert_eq!` statements can be disabled by
173 /// passing `--cfg ndebug` to the compiler. This makes `debug_assert_eq!`
174 /// useful for checks that are too expensive to be present in a release build
175 /// but may be helpful during development.
182 /// debug_assert_eq!(a, b);
185 macro_rules! debug_assert_eq(
186 ($($arg:tt)*) => (if cfg!(not(ndebug)) { assert_eq!($($arg)*); })
189 /// A utility macro for indicating unreachable code. It will panic if
190 /// executed. This is occasionally useful to put after loops that never
191 /// terminate normally, but instead directly return from a function.
196 /// struct Item { weight: uint }
198 /// fn choose_weighted_item(v: &[Item]) -> Item {
199 /// assert!(!v.is_empty());
200 /// let mut so_far = 0u;
201 /// for item in v.iter() {
202 /// so_far += item.weight;
203 /// if so_far > 100 {
207 /// // The above loop always returns, so we must hint to the
208 /// // type checker that it isn't possible to get down here
213 macro_rules! unreachable(
215 panic!("internal error: entered unreachable code")
218 unreachable!("{}", $msg)
220 ($fmt:expr, $($arg:tt)*) => ({
221 panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
225 /// A standardised placeholder for marking unfinished code. It panics with the
226 /// message `"not yet implemented"` when executed.
228 macro_rules! unimplemented(
229 () => (panic!("not yet implemented"))
232 /// Use the syntax described in `std::fmt` to create a value of type `String`.
233 /// See `std::fmt` for more information.
239 /// format!("hello {}", "world!");
240 /// format!("x = {}, y = {y}", 10i, y = 30i);
246 format_args!(::std::fmt::format, $($arg)*)
250 /// Use the `format!` syntax to write data into a buffer of type `&mut Writer`.
251 /// See `std::fmt` for more information.
256 /// # #![allow(unused_must_use)]
258 /// let mut w = Vec::new();
259 /// write!(&mut w, "test");
260 /// write!(&mut w, "formatted {}", "arguments");
265 ($dst:expr, $($arg:tt)*) => ({
266 let dst = &mut *$dst;
267 format_args!(|args| { dst.write_fmt(args) }, $($arg)*)
271 /// Equivalent to the `write!` macro, except that a newline is appended after
272 /// the message is written.
275 macro_rules! writeln(
276 ($dst:expr, $fmt:expr $($arg:tt)*) => (
277 write!($dst, concat!($fmt, "\n") $($arg)*)
281 /// Equivalent to the `println!` macro except that a newline is not printed at
282 /// the end of the message.
286 ($($arg:tt)*) => (format_args!(::std::io::stdio::print_args, $($arg)*))
289 /// Macro for printing to a task's stdout handle.
291 /// Each task can override its stdout handle via `std::io::stdio::set_stdout`.
292 /// The syntax of this macro is the same as that used for `format!`. For more
293 /// information, see `std::fmt` and `std::io::stdio`.
298 /// println!("hello there!");
299 /// println!("format {} arguments", "some");
303 macro_rules! println(
304 ($($arg:tt)*) => (format_args!(::std::io::stdio::println_args, $($arg)*))
307 /// Helper macro for unwrapping `Result` values while returning early with an
308 /// error if the value of the expression is `Err`. For more information, see
315 Err(err) => return Err(::std::error::FromError::from_error(err))
320 /// Create a `std::vec::Vec` containing the arguments.
324 use std::slice::BoxedSlicePrelude;
325 let xs: ::std::boxed::Box<[_]> = box [$($x),*];
328 ($($x:expr,)*) => (vec![$($x),*])
331 /// A macro to select an event from a number of receivers.
333 /// This macro is used to wait for the first event to occur on a number of
334 /// receivers. It places no restrictions on the types of receivers given to
335 /// this macro, this can be viewed as a heterogeneous select.
340 /// let (tx1, rx1) = channel();
341 /// let (tx2, rx2) = channel();
342 /// # fn long_running_task() {}
343 /// # fn calculate_the_answer() -> int { 42i }
345 /// spawn(proc() { long_running_task(); tx1.send(()) });
346 /// spawn(proc() { tx2.send(calculate_the_answer()) });
349 /// () = rx1.recv() => println!("the long running task finished first"),
350 /// answer = rx2.recv() => {
351 /// println!("the answer was: {}", answer);
356 /// For more information about select, see the `std::comm::Select` structure.
359 macro_rules! select {
361 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
363 use std::comm::Select;
364 let sel = Select::new();
365 $( let mut $rx = sel.handle(&$rx); )+
369 let ret = sel.wait();
370 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
375 // When testing the standard library, we link to the liblog crate to get the
376 // logging macros. In doing so, the liblog crate was linked against the real
377 // version of libstd, and uses a different std::fmt module than the test crate
378 // uses. To get around this difference, we redefine the log!() macro here to be
379 // just a dumb version of what it should be.
382 ($lvl:expr, $($args:tt)*) => (
383 if log_enabled!($lvl) { println!($($args)*) }
387 /// Built-in macros to the compiler itself.
389 /// These macros do not have any corresponding definition with a `macro_rules!`
390 /// macro, but are documented here. Their implementations can be found hardcoded
391 /// into libsyntax itself.
394 /// The core macro for formatted string creation & output.
396 /// This macro takes as its first argument a callable expression which will
397 /// receive as its first argument a value of type `&fmt::Arguments`. This
398 /// value can be passed to the functions in `std::fmt` for performing useful
399 /// functions. All other formatting macros (`format!`, `write!`,
400 /// `println!`, etc) are proxied through this one.
402 /// For more information, see the documentation in `std::fmt`.
409 /// let s = format_args!(fmt::format, "hello {}", "world");
410 /// assert_eq!(s, format!("hello {}", "world"));
412 /// format_args!(|args| {
413 /// // pass `args` to another function, etc.
414 /// }, "hello {}", "world");
417 macro_rules! format_args( ($closure:expr, $fmt:expr $($args:tt)*) => ({
418 /* compiler built-in */
421 /// Inspect an environment variable at compile time.
423 /// This macro will expand to the value of the named environment variable at
424 /// compile time, yielding an expression of type `&'static str`.
426 /// If the environment variable is not defined, then a compilation error
427 /// will be emitted. To not emit a compile error, use the `option_env!`
433 /// let path: &'static str = env!("PATH");
434 /// println!("the $PATH variable at the time of compiling was: {}", path);
437 macro_rules! env( ($name:expr) => ({ /* compiler built-in */ }) )
439 /// Optionally inspect an environment variable at compile time.
441 /// If the named environment variable is present at compile time, this will
442 /// expand into an expression of type `Option<&'static str>` whose value is
443 /// `Some` of the value of the environment variable. If the environment
444 /// variable is not present, then this will expand to `None`.
446 /// A compile time error is never emitted when using this macro regardless
447 /// of whether the environment variable is present or not.
452 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
453 /// println!("the secret key might be: {}", key);
456 macro_rules! option_env( ($name:expr) => ({ /* compiler built-in */ }) )
458 /// Concatenate literals into a static byte slice.
460 /// This macro takes any number of comma-separated literal expressions,
461 /// yielding an expression of type `&'static [u8]` which is the
462 /// concatenation (left to right) of all the literals in their byte format.
464 /// This extension currently only supports string literals, character
465 /// literals, and integers less than 256. The byte slice returned is the
466 /// utf8-encoding of strings and characters.
471 /// let rust = bytes!("r", 'u', "st", 255);
472 /// assert_eq!(rust[1], b'u');
473 /// assert_eq!(rust[4], 255);
476 macro_rules! bytes( ($($e:expr),*) => ({ /* compiler built-in */ }) )
478 /// Concatenate identifiers into one identifier.
480 /// This macro takes any number of comma-separated identifiers, and
481 /// concatenates them all into one, yielding an expression which is a new
482 /// identifier. Note that hygiene makes it such that this macro cannot
483 /// capture local variables, and macros are only allowed in item,
484 /// statement or expression position, meaning this macro may be difficult to
485 /// use in some situations.
490 /// #![feature(concat_idents)]
493 /// fn foobar() -> int { 23 }
495 /// let f = concat_idents!(foo, bar);
496 /// println!("{}", f());
500 macro_rules! concat_idents( ($($e:ident),*) => ({ /* compiler built-in */ }) )
502 /// Concatenates literals into a static string slice.
504 /// This macro takes any number of comma-separated literals, yielding an
505 /// expression of type `&'static str` which represents all of the literals
506 /// concatenated left-to-right.
508 /// Integer and floating point literals are stringified in order to be
514 /// let s = concat!("test", 10i, 'b', true);
515 /// assert_eq!(s, "test10btrue");
518 macro_rules! concat( ($($e:expr),*) => ({ /* compiler built-in */ }) )
520 /// A macro which expands to the line number on which it was invoked.
522 /// The expanded expression has type `uint`, and the returned line is not
523 /// the invocation of the `line!()` macro itself, but rather the first macro
524 /// invocation leading up to the invocation of the `line!()` macro.
529 /// let current_line = line!();
530 /// println!("defined on line: {}", current_line);
533 macro_rules! line( () => ({ /* compiler built-in */ }) )
535 /// A macro which expands to the column number on which it was invoked.
537 /// The expanded expression has type `uint`, and the returned column is not
538 /// the invocation of the `column!()` macro itself, but rather the first macro
539 /// invocation leading up to the invocation of the `column!()` macro.
544 /// let current_col = column!();
545 /// println!("defined on column: {}", current_col);
548 macro_rules! column( () => ({ /* compiler built-in */ }) )
550 /// A macro which expands to the file name from which it was invoked.
552 /// The expanded expression has type `&'static str`, and the returned file
553 /// is not the invocation of the `file!()` macro itself, but rather the
554 /// first macro invocation leading up to the invocation of the `file!()`
560 /// let this_file = file!();
561 /// println!("defined in file: {}", this_file);
564 macro_rules! file( () => ({ /* compiler built-in */ }) )
566 /// A macro which stringifies its argument.
568 /// This macro will yield an expression of type `&'static str` which is the
569 /// stringification of all the tokens passed to the macro. No restrictions
570 /// are placed on the syntax of the macro invocation itself.
575 /// let one_plus_one = stringify!(1 + 1);
576 /// assert_eq!(one_plus_one, "1 + 1");
579 macro_rules! stringify( ($t:tt) => ({ /* compiler built-in */ }) )
581 /// Includes a utf8-encoded file as a string.
583 /// This macro will yield an expression of type `&'static str` which is the
584 /// contents of the filename specified. The file is located relative to the
585 /// current file (similarly to how modules are found),
590 /// let secret_key = include_str!("secret-key.ascii");
593 macro_rules! include_str( ($file:expr) => ({ /* compiler built-in */ }) )
595 /// Includes a file as a byte slice.
597 /// This macro will yield an expression of type `&'static [u8]` which is
598 /// the contents of the filename specified. The file is located relative to
599 /// the current file (similarly to how modules are found),
604 /// let secret_key = include_bin!("secret-key.bin");
607 macro_rules! include_bin( ($file:expr) => ({ /* compiler built-in */ }) )
609 /// Expands to a string that represents the current module path.
611 /// The current module path can be thought of as the hierarchy of modules
612 /// leading back up to the crate root. The first component of the path
613 /// returned is the name of the crate currently being compiled.
620 /// assert!(module_path!().ends_with("test"));
627 macro_rules! module_path( () => ({ /* compiler built-in */ }) )
629 /// Boolean evaluation of configuration flags.
631 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
632 /// boolean expression evaluation of configuration flags. This frequently
633 /// leads to less duplicated code.
635 /// The syntax given to this macro is the same syntax as the `cfg`
641 /// let my_directory = if cfg!(windows) {
642 /// "windows-specific-directory"
648 macro_rules! cfg( ($cfg:tt) => ({ /* compiler built-in */ }) )