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(
214 () => (panic!("internal error: entered unreachable code"))
217 /// A standardised placeholder for marking unfinished code. It panics with the
218 /// message `"not yet implemented"` when executed.
220 macro_rules! unimplemented(
221 () => (panic!("not yet implemented"))
224 /// Use the syntax described in `std::fmt` to create a value of type `String`.
225 /// See `std::fmt` for more information.
231 /// format!("hello {}", "world!");
232 /// format!("x = {}, y = {y}", 10i, y = 30i);
237 format_args!(::std::fmt::format, $($arg)*)
241 /// Use the `format!` syntax to write data into a buffer of type `&mut Writer`.
242 /// See `std::fmt` for more information.
247 /// # #![allow(unused_must_use)]
248 /// use std::io::MemWriter;
250 /// let mut w = MemWriter::new();
251 /// write!(&mut w, "test");
252 /// write!(&mut w, "formatted {}", "arguments");
256 ($dst:expr, $($arg:tt)*) => ({
257 format_args_method!($dst, write_fmt, $($arg)*)
261 /// Equivalent to the `write!` macro, except that a newline is appended after
262 /// the message is written.
264 macro_rules! writeln(
265 ($dst:expr, $fmt:expr $($arg:tt)*) => (
266 write!($dst, concat!($fmt, "\n") $($arg)*)
270 /// Equivalent to the `println!` macro except that a newline is not printed at
271 /// the end of the message.
274 ($($arg:tt)*) => (format_args!(::std::io::stdio::print_args, $($arg)*))
277 /// Macro for printing to a task's stdout handle.
279 /// Each task can override its stdout handle via `std::io::stdio::set_stdout`.
280 /// The syntax of this macro is the same as that used for `format!`. For more
281 /// information, see `std::fmt` and `std::io::stdio`.
286 /// println!("hello there!");
287 /// println!("format {} arguments", "some");
290 macro_rules! println(
291 ($($arg:tt)*) => (format_args!(::std::io::stdio::println_args, $($arg)*))
294 /// Declare a task-local key with a specific type.
299 /// local_data_key!(my_integer: int)
301 /// my_integer.replace(Some(2));
302 /// println!("{}", my_integer.get().map(|a| *a));
305 macro_rules! local_data_key(
306 ($name:ident: $ty:ty) => (
307 #[allow(non_upper_case_globals)]
308 static $name: ::std::local_data::Key<$ty> = &::std::local_data::KeyValueKey;
310 (pub $name:ident: $ty:ty) => (
311 #[allow(non_upper_case_globals)]
312 pub static $name: ::std::local_data::Key<$ty> = &::std::local_data::KeyValueKey;
316 /// Helper macro for unwrapping `Result` values while returning early with an
317 /// error if the value of the expression is `Err`. For more information, see
324 Err(err) => return Err(::std::error::FromError::from_error(err))
329 /// Create a `std::vec::Vec` containing the arguments.
333 use std::slice::BoxedSlice;
334 let xs: ::std::boxed::Box<[_]> = box [$($x),*];
337 ($($x:expr,)*) => (vec![$($x),*])
340 /// A macro to select an event from a number of receivers.
342 /// This macro is used to wait for the first event to occur on a number of
343 /// receivers. It places no restrictions on the types of receivers given to
344 /// this macro, this can be viewed as a heterogeneous select.
349 /// let (tx1, rx1) = channel();
350 /// let (tx2, rx2) = channel();
351 /// # fn long_running_task() {}
352 /// # fn calculate_the_answer() -> int { 42i }
354 /// spawn(proc() { long_running_task(); tx1.send(()) });
355 /// spawn(proc() { tx2.send(calculate_the_answer()) });
358 /// () = rx1.recv() => println!("the long running task finished first"),
359 /// answer = rx2.recv() => {
360 /// println!("the answer was: {}", answer);
365 /// For more information about select, see the `std::comm::Select` structure.
368 macro_rules! select {
370 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
372 use std::comm::Select;
373 let sel = Select::new();
374 $( let mut $rx = sel.handle(&$rx); )+
378 let ret = sel.wait();
379 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
384 // When testing the standard library, we link to the liblog crate to get the
385 // logging macros. In doing so, the liblog crate was linked against the real
386 // version of libstd, and uses a different std::fmt module than the test crate
387 // uses. To get around this difference, we redefine the log!() macro here to be
388 // just a dumb version of what it should be.
391 ($lvl:expr, $($args:tt)*) => (
392 if log_enabled!($lvl) { println!($($args)*) }
396 /// Built-in macros to the compiler itself.
398 /// These macros do not have any corresponding definition with a `macro_rules!`
399 /// macro, but are documented here. Their implementations can be found hardcoded
400 /// into libsyntax itself.
403 /// The core macro for formatted string creation & output.
405 /// This macro takes as its first argument a callable expression which will
406 /// receive as its first argument a value of type `&fmt::Arguments`. This
407 /// value can be passed to the functions in `std::fmt` for performing useful
408 /// functions. All other formatting macros (`format!`, `write!`,
409 /// `println!`, etc) are proxied through this one.
411 /// For more information, see the documentation in `std::fmt`.
418 /// let s = format_args!(fmt::format, "hello {}", "world");
419 /// assert_eq!(s, format!("hello {}", "world"));
421 /// format_args!(|args| {
422 /// // pass `args` to another function, etc.
423 /// }, "hello {}", "world");
426 macro_rules! format_args( ($closure:expr, $fmt:expr $($args:tt)*) => ({
427 /* compiler built-in */
430 /// Inspect an environment variable at compile time.
432 /// This macro will expand to the value of the named environment variable at
433 /// compile time, yielding an expression of type `&'static str`.
435 /// If the environment variable is not defined, then a compilation error
436 /// will be emitted. To not emit a compile error, use the `option_env!`
442 /// let path: &'static str = env!("PATH");
443 /// println!("the $PATH variable at the time of compiling was: {}", path);
446 macro_rules! env( ($name:expr) => ({ /* compiler built-in */ }) )
448 /// Optionally inspect an environment variable at compile time.
450 /// If the named environment variable is present at compile time, this will
451 /// expand into an expression of type `Option<&'static str>` whose value is
452 /// `Some` of the value of the environment variable. If the environment
453 /// variable is not present, then this will expand to `None`.
455 /// A compile time error is never emitted when using this macro regardless
456 /// of whether the environment variable is present or not.
461 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
462 /// println!("the secret key might be: {}", key);
465 macro_rules! option_env( ($name:expr) => ({ /* compiler built-in */ }) )
467 /// Concatenate literals into a static byte slice.
469 /// This macro takes any number of comma-separated literal expressions,
470 /// yielding an expression of type `&'static [u8]` which is the
471 /// concatenation (left to right) of all the literals in their byte format.
473 /// This extension currently only supports string literals, character
474 /// literals, and integers less than 256. The byte slice returned is the
475 /// utf8-encoding of strings and characters.
480 /// let rust = bytes!("r", 'u', "st", 255);
481 /// assert_eq!(rust[1], b'u');
482 /// assert_eq!(rust[4], 255);
485 macro_rules! bytes( ($($e:expr),*) => ({ /* compiler built-in */ }) )
487 /// Concatenate identifiers into one identifier.
489 /// This macro takes any number of comma-separated identifiers, and
490 /// concatenates them all into one, yielding an expression which is a new
491 /// identifier. Note that hygiene makes it such that this macro cannot
492 /// capture local variables, and macros are only allowed in item,
493 /// statement or expression position, meaning this macro may be difficult to
494 /// use in some situations.
499 /// #![feature(concat_idents)]
502 /// fn foobar() -> int { 23 }
504 /// let f = concat_idents!(foo, bar);
505 /// println!("{}", f());
509 macro_rules! concat_idents( ($($e:ident),*) => ({ /* compiler built-in */ }) )
511 /// Concatenates literals into a static string slice.
513 /// This macro takes any number of comma-separated literals, yielding an
514 /// expression of type `&'static str` which represents all of the literals
515 /// concatenated left-to-right.
517 /// Integer and floating point literals are stringified in order to be
523 /// let s = concat!("test", 10i, 'b', true);
524 /// assert_eq!(s, "test10btrue");
527 macro_rules! concat( ($($e:expr),*) => ({ /* compiler built-in */ }) )
529 /// A macro which expands to the line number on which it was invoked.
531 /// The expanded expression has type `uint`, and the returned line is not
532 /// the invocation of the `line!()` macro itself, but rather the first macro
533 /// invocation leading up to the invocation of the `line!()` macro.
538 /// let current_line = line!();
539 /// println!("defined on line: {}", current_line);
542 macro_rules! line( () => ({ /* compiler built-in */ }) )
544 /// A macro which expands to the column number on which it was invoked.
546 /// The expanded expression has type `uint`, and the returned column is not
547 /// the invocation of the `col!()` macro itself, but rather the first macro
548 /// invocation leading up to the invocation of the `col!()` macro.
553 /// let current_col = col!();
554 /// println!("defined on column: {}", current_col);
557 macro_rules! col( () => ({ /* compiler built-in */ }) )
559 /// A macro which expands to the file name from which it was invoked.
561 /// The expanded expression has type `&'static str`, and the returned file
562 /// is not the invocation of the `file!()` macro itself, but rather the
563 /// first macro invocation leading up to the invocation of the `file!()`
569 /// let this_file = file!();
570 /// println!("defined in file: {}", this_file);
573 macro_rules! file( () => ({ /* compiler built-in */ }) )
575 /// A macro which stringifies its argument.
577 /// This macro will yield an expression of type `&'static str` which is the
578 /// stringification of all the tokens passed to the macro. No restrictions
579 /// are placed on the syntax of the macro invocation itself.
584 /// let one_plus_one = stringify!(1 + 1);
585 /// assert_eq!(one_plus_one, "1 + 1");
588 macro_rules! stringify( ($t:tt) => ({ /* compiler built-in */ }) )
590 /// Includes a utf8-encoded file as a string.
592 /// This macro will yield an expression of type `&'static str` which is the
593 /// contents of the filename specified. The file is located relative to the
594 /// current file (similarly to how modules are found),
599 /// let secret_key = include_str!("secret-key.ascii");
602 macro_rules! include_str( ($file:expr) => ({ /* compiler built-in */ }) )
604 /// Includes a file as a byte slice.
606 /// This macro will yield an expression of type `&'static [u8]` which is
607 /// the contents of the filename specified. The file is located relative to
608 /// the current file (similarly to how modules are found),
613 /// let secret_key = include_bin!("secret-key.bin");
616 macro_rules! include_bin( ($file:expr) => ({ /* compiler built-in */ }) )
618 /// Expands to a string that represents the current module path.
620 /// The current module path can be thought of as the hierarchy of modules
621 /// leading back up to the crate root. The first component of the path
622 /// returned is the name of the crate currently being compiled.
629 /// assert!(module_path!().ends_with("test"));
636 macro_rules! module_path( () => ({ /* compiler built-in */ }) )
638 /// Boolean evaluation of configuration flags.
640 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
641 /// boolean expression evaluation of configuration flags. This frequently
642 /// leads to less duplicated code.
644 /// The syntax given to this macro is the same syntax as the `cfg`
650 /// let my_directory = if cfg!(windows) {
651 /// "windows-specific-directory"
657 macro_rules! cfg( ($cfg:tt) => ({ /* compiler built-in */ }) )