(index<- ) ./libstd/macros.rs
git branch: * master 5200215 auto merge of #14035 : alexcrichton/rust/experimental, r=huonw
modified: Fri May 9 13:02:28 2014
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
4 //
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.
10
11 //! Standard library macros
12 //!
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
15 //! library.
16
17 #![macro_escape]
18
19 /// The entry point for failure of rust tasks.
20 ///
21 /// This macro is used to inject failure into a rust task, causing the task to
22 /// unwind and fail entirely. Each task's failure can be reaped as the
23 /// `Box<Any>` type, and the single-argument form of the `fail!` macro will be
24 /// the value which is transmitted.
25 ///
26 /// The multi-argument form of this macro fails with a string and has the
27 /// `format!` syntax for building a string.
28 ///
29 /// # Example
30 ///
31 /// ```should_fail
32 /// # #![allow(unreachable_code)]
33 /// fail!();
34 /// fail!("this is a terrible mistake!");
35 /// fail!(4); // fail with the value of 4 to be collected elsewhere
36 /// fail!("this is a {} {message}", "fancy", message = "message");
37 /// ```
38 #[macro_export]
39 macro_rules! fail(
40 () => (
41 fail!("explicit failure")
42 );
43 ($msg:expr) => (
44 ::std::rt::begin_unwind($msg, file!(), line!())
45 );
46 ($fmt:expr, $($arg:tt)*) => ({
47 // a closure can't have return type !, so we need a full
48 // function to pass to format_args!, *and* we need the
49 // file and line numbers right here; so an inner bare fn
50 // is our only choice.
51 //
52 // LLVM doesn't tend to inline this, presumably because begin_unwind_fmt
53 // is #[cold] and #[inline(never)] and because this is flagged as cold
54 // as returning !. We really do want this to be inlined, however,
55 // because it's just a tiny wrapper. Small wins (156K to 149K in size)
56 // were seen when forcing this to be inlined, and that number just goes
57 // up with the number of calls to fail!()
58 #[inline(always)]
59 fn run_fmt(fmt: &::std::fmt::Arguments) -> ! {
60 ::std::rt::begin_unwind_fmt(fmt, file!(), line!())
61 }
62 format_args!(run_fmt, $fmt, $($arg)*)
63 });
64 )
65
66 /// Ensure that a boolean expression is `true` at runtime.
67 ///
68 /// This will invoke the `fail!` macro if the provided expression cannot be
69 /// evaluated to `true` at runtime.
70 ///
71 /// # Example
72 ///
73 /// ```
74 /// // the failure message for these assertions is the stringified value of the
75 /// // expression given.
76 /// assert!(true);
77 /// # fn some_computation() -> bool { true }
78 /// assert!(some_computation());
79 ///
80 /// // assert with a custom message
81 /// # let x = true;
82 /// assert!(x, "x wasn't true!");
83 /// # let a = 3; let b = 27;
84 /// assert!(a + b == 30, "a = {}, b = {}", a, b);
85 /// ```
86 #[macro_export]
87 macro_rules! assert(
88 ($cond:expr) => (
89 if !$cond {
90 fail!("assertion failed: {:s}", stringify!($cond))
91 }
92 );
93 ($cond:expr, $($arg:expr),+) => (
94 if !$cond {
95 fail!($($arg),+)
96 }
97 );
98 )
99
100 /// Asserts that two expressions are equal to each other, testing equality in
101 /// both directions.
102 ///
103 /// On failure, this macro will print the values of the expressions.
104 ///
105 /// # Example
106 ///
107 /// ```
108 /// let a = 3;
109 /// let b = 1 + 2;
110 /// assert_eq!(a, b);
111 /// ```
112 #[macro_export]
113 macro_rules! assert_eq(
114 ($given:expr , $expected:expr) => ({
115 match (&($given), &($expected)) {
116 (given_val, expected_val) => {
117 // check both directions of equality....
118 if !((*given_val == *expected_val) &&
119 (*expected_val == *given_val)) {
120 fail!("assertion failed: `(left == right) && (right == left)` \
121 (left: `{}`, right: `{}`)", *given_val, *expected_val)
122 }
123 }
124 }
125 })
126 )
127
128 /// Ensure that a boolean expression is `true` at runtime.
129 ///
130 /// This will invoke the `fail!` macro if the provided expression cannot be
131 /// evaluated to `true` at runtime.
132 ///
133 /// Unlike `assert!`, `debug_assert!` statements can be disabled by passing
134 /// `--cfg ndebug` to the compiler. This makes `debug_assert!` useful for
135 /// checks that are too expensive to be present in a release build but may be
136 /// helpful during development.
137 ///
138 /// # Example
139 ///
140 /// ```
141 /// // the failure message for these assertions is the stringified value of the
142 /// // expression given.
143 /// debug_assert!(true);
144 /// # fn some_expensive_computation() -> bool { true }
145 /// debug_assert!(some_expensive_computation());
146 ///
147 /// // assert with a custom message
148 /// # let x = true;
149 /// debug_assert!(x, "x wasn't true!");
150 /// # let a = 3; let b = 27;
151 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
152 /// ```
153 #[macro_export]
154 macro_rules! debug_assert(
155 ($($arg:tt)*) => (if cfg!(not(ndebug)) { assert!($($arg)*); })
156 )
157
158 /// Asserts that two expressions are equal to each other, testing equality in
159 /// both directions.
160 ///
161 /// On failure, this macro will print the values of the expressions.
162 ///
163 /// Unlike `assert_eq!`, `debug_assert_eq!` statements can be disabled by
164 /// passing `--cfg ndebug` to the compiler. This makes `debug_assert_eq!`
165 /// useful for checks that are too expensive to be present in a release build
166 /// but may be helpful during development.
167 ///
168 /// # Example
169 ///
170 /// ```
171 /// let a = 3;
172 /// let b = 1 + 2;
173 /// debug_assert_eq!(a, b);
174 /// ```
175 #[macro_export]
176 macro_rules! debug_assert_eq(
177 ($($arg:tt)*) => (if cfg!(not(ndebug)) { assert_eq!($($arg)*); })
178 )
179
180 /// A utility macro for indicating unreachable code. It will fail if
181 /// executed. This is occasionally useful to put after loops that never
182 /// terminate normally, but instead directly return from a function.
183 ///
184 /// # Example
185 ///
186 /// ~~~rust
187 /// struct Item { weight: uint }
188 ///
189 /// fn choose_weighted_item(v: &[Item]) -> Item {
190 /// assert!(!v.is_empty());
191 /// let mut so_far = 0u;
192 /// for item in v.iter() {
193 /// so_far += item.weight;
194 /// if so_far > 100 {
195 /// return *item;
196 /// }
197 /// }
198 /// // The above loop always returns, so we must hint to the
199 /// // type checker that it isn't possible to get down here
200 /// unreachable!();
201 /// }
202 /// ~~~
203 #[macro_export]
204 macro_rules! unreachable(
205 () => (fail!("internal error: entered unreachable code"))
206 )
207
208 /// A standardised placeholder for marking unfinished code. It fails with the
209 /// message `"not yet implemented"` when executed.
210 #[macro_export]
211 macro_rules! unimplemented(
212 () => (fail!("not yet implemented"))
213 )
214
215 /// Use the syntax described in `std::fmt` to create a value of type `~str`.
216 /// See `std::fmt` for more information.
217 ///
218 /// # Example
219 ///
220 /// ```
221 /// format!("test");
222 /// format!("hello {}", "world!");
223 /// format!("x = {}, y = {y}", 10, y = 30);
224 /// ```
225 #[macro_export]
226 macro_rules! format(
227 ($($arg:tt)*) => (
228 format_args!(::std::fmt::format, $($arg)*)
229 )
230 )
231
232 /// Use the `format!` syntax to write data into a buffer of type `&mut Writer`.
233 /// See `std::fmt` for more information.
234 ///
235 /// # Example
236 ///
237 /// ```
238 /// # #![allow(unused_must_use)]
239 /// use std::io::MemWriter;
240 ///
241 /// let mut w = MemWriter::new();
242 /// write!(&mut w, "test");
243 /// write!(&mut w, "formatted {}", "arguments");
244 /// ```
245 #[macro_export]
246 macro_rules! write(
247 ($dst:expr, $($arg:tt)*) => ({
248 let dst: &mut ::std::io::Writer = $dst;
249 format_args!(|args| { ::std::fmt::write(dst, args) }, $($arg)*)
250 })
251 )
252
253 /// Equivalent to the `write!` macro, except that a newline is appended after
254 /// the message is written.
255 #[macro_export]
256 macro_rules! writeln(
257 ($dst:expr, $($arg:tt)*) => ({
258 let dst: &mut ::std::io::Writer = $dst;
259 format_args!(|args| { ::std::fmt::writeln(dst, args) }, $($arg)*)
260 })
261 )
262
263 /// Equivalent to the `println!` macro except that a newline is not printed at
264 /// the end of the message.
265 #[macro_export]
266 macro_rules! print(
267 ($($arg:tt)*) => (format_args!(::std::io::stdio::print_args, $($arg)*))
268 )
269
270 /// Macro for printing to a task's stdout handle.
271 ///
272 /// Each task can override its stdout handle via `std::io::stdio::set_stdout`.
273 /// The syntax of this macro is the same as that used for `format!`. For more
274 /// information, see `std::fmt` and `std::io::stdio`.
275 ///
276 /// # Example
277 ///
278 /// ```
279 /// println!("hello there!");
280 /// println!("format {} arguments", "some");
281 /// ```
282 #[macro_export]
283 macro_rules! println(
284 ($($arg:tt)*) => (format_args!(::std::io::stdio::println_args, $($arg)*))
285 )
286
287 /// Declare a task-local key with a specific type.
288 ///
289 /// # Example
290 ///
291 /// ```
292 /// local_data_key!(my_integer: int)
293 ///
294 /// my_integer.replace(Some(2));
295 /// println!("{}", my_integer.get().map(|a| *a));
296 /// ```
297 #[macro_export]
298 macro_rules! local_data_key(
299 ($name:ident: $ty:ty) => (
300 static $name: ::std::local_data::Key<$ty> = &::std::local_data::Key;
301 );
302 (pub $name:ident: $ty:ty) => (
303 pub static $name: ::std::local_data::Key<$ty> = &::std::local_data::Key;
304 );
305 )
306
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
309 /// `std::io`.
310 #[macro_export]
311 macro_rules! try(
312 ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
313 )
314
315 /// Create a `std::vec::Vec` containing the arguments.
316 #[macro_export]
317 macro_rules! vec(
318 ($($e:expr),*) => ({
319 // leading _ to allow empty construction without a warning.
320 let mut _temp = ::std::vec::Vec::new();
321 $(_temp.push($e);)*
322 _temp
323 });
324 ($($e:expr),+,) => (vec!($($e),+))
325 )
326
327
328 /// A macro to select an event from a number of ports.
329 ///
330 /// This macro is used to wait for the first event to occur on a number of
331 /// ports. It places no restrictions on the types of ports given to this macro,
332 /// this can be viewed as a heterogeneous select.
333 ///
334 /// # Example
335 ///
336 /// ```
337 /// let (tx1, rx1) = channel();
338 /// let (tx2, rx2) = channel();
339 /// # fn long_running_task() {}
340 /// # fn calculate_the_answer() -> int { 42 }
341 ///
342 /// spawn(proc() { long_running_task(); tx1.send(()) });
343 /// spawn(proc() { tx2.send(calculate_the_answer()) });
344 ///
345 /// select! (
346 /// () = rx1.recv() => println!("the long running task finished first"),
347 /// answer = rx2.recv() => {
348 /// println!("the answer was: {}", answer);
349 /// }
350 /// )
351 /// ```
352 ///
353 /// For more information about select, see the `std::comm::Select` structure.
354 #[macro_export]
355 #[experimental]
356 macro_rules! select {
357 (
358 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
359 ) => ({
360 use std::comm::Select;
361 let sel = Select::new();
362 $( let mut $rx = sel.handle(&$rx); )+
363 unsafe {
364 $( $rx.add(); )+
365 }
366 let ret = sel.wait();
367 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
368 { unreachable!() }
369 })
370 }
371
372 // When testing the standard library, we link to the liblog crate to get the
373 // logging macros. In doing so, the liblog crate was linked against the real
374 // version of libstd, and uses a different std::fmt module than the test crate
375 // uses. To get around this difference, we redefine the log!() macro here to be
376 // just a dumb version of what it should be.
377 #[cfg(test)]
378 macro_rules! log (
379 ($lvl:expr, $($args:tt)*) => (
380 if log_enabled!($lvl) { println!($($args)*) }
381 )
382 )
383
384 /// Built-in macros to the compiler itself.
385 ///
386 /// These macros do not have any corresponding definition with a `macro_rules!`
387 /// macro, but are documented here. Their implementations can be found hardcoded
388 /// into libsyntax itself.
389 #[cfg(dox)]
390 pub mod builtin {
391 /// The core macro for formatted string creation & output.
392 ///
393 /// This macro takes as its first argument a callable expression which will
394 /// receive as its first argument a value of type `&fmt::Arguments`. This
395 /// value can be passed to the functions in `std::fmt` for performing useful
396 /// functions. All other formatting macros (`format!`, `write!`,
397 /// `println!`, etc) are proxied through this one.
398 ///
399 /// For more information, see the documentation in `std::fmt`.
400 ///
401 /// # Example
402 ///
403 /// ```rust
404 /// use std::fmt;
405 ///
406 /// let s = format_args!(fmt::format, "hello {}", "world");
407 /// assert_eq!(s, format!("hello {}", "world"));
408 ///
409 /// format_args!(|args| {
410 /// // pass `args` to another function, etc.
411 /// }, "hello {}", "world");
412 /// ```
413 #[macro_export]
414 macro_rules! format_args( ($closure:expr, $fmt:expr $($args:tt)*) => ({
415 /* compiler built-in */
416 }) )
417
418 /// Inspect an environment variable at compile time.
419 ///
420 /// This macro will expand to the value of the named environment variable at
421 /// compile time, yielding an expression of type `&'static str`.
422 ///
423 /// If the environment variable is not defined, then a compilation error
424 /// will be emitted. To not emit a compile error, use the `option_env!`
425 /// macro instead.
426 ///
427 /// # Example
428 ///
429 /// ```rust
430 /// let user: &'static str = env!("USER");
431 /// println!("the user who compiled this code is: {}", user);
432 /// ```
433 #[macro_export]
434 macro_rules! env( ($name:expr) => ({ /* compiler built-in */ }) )
435
436 /// Optionally inspect an environment variable at compile time.
437 ///
438 /// If the named environment variable is present at compile time, this will
439 /// expand into an expression of type `Option<&'static str>` whose value is
440 /// `Some` of the value of the environment variable. If the environment
441 /// variable is not present, then this will expand to `None`.
442 ///
443 /// A compile time error is never emitted when using this macro regardless
444 /// of whether the environment variable is present or not.
445 ///
446 /// # Example
447 ///
448 /// ```rust
449 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
450 /// println!("the secret key might be: {}", key);
451 /// ```
452 #[macro_export]
453 macro_rules! option_env( ($name:expr) => ({ /* compiler built-in */ }) )
454
455 /// Concatenate literals into a static byte slice.
456 ///
457 /// This macro takes any number of comma-separated literal expressions,
458 /// yielding an expression of type `&'static [u8]` which is the
459 /// concatenation (left to right) of all the literals in their byte format.
460 ///
461 /// This extension currently only supports string literals, character
462 /// literals, and integers less than 256. The byte slice returned is the
463 /// utf8-encoding of strings and characters.
464 ///
465 /// # Example
466 ///
467 /// ```
468 /// let rust = bytes!("r", 'u', "st");
469 /// assert_eq!(rust[1], 'u' as u8);
470 /// ```
471 #[macro_export]
472 macro_rules! bytes( ($($e:expr),*) => ({ /* compiler built-in */ }) )
473
474 /// Concatenate identifiers into one identifier.
475 ///
476 /// This macro takes any number of comma-separated identifiers, and
477 /// concatenates them all into one, yielding an expression which is a new
478 /// identifier. Note that hygiene makes it such that this macro cannot
479 /// capture local variables, and macros are only allowed in item,
480 /// statement or expression position, meaning this macro may be difficult to
481 /// use in some situations.
482 ///
483 /// # Example
484 ///
485 /// ```
486 /// fn foobar() -> int { 23 }
487 ///
488 /// let f = concat_idents!(foo, bar);
489 /// println!("{}", f());
490 /// ```
491 #[macro_export]
492 macro_rules! concat_idents( ($($e:ident),*) => ({ /* compiler built-in */ }) )
493
494 /// Concatenates literals into a static string slice.
495 ///
496 /// This macro takes any number of comma-separated literals, yielding an
497 /// expression of type `&'static str` which represents all of the literals
498 /// concatenated left-to-right.
499 ///
500 /// Integer and floating point literals are stringified in order to be
501 /// concatenated.
502 ///
503 /// # Example
504 ///
505 /// ```
506 /// let s = concat!("test", 10, 'b', true);
507 /// assert_eq!(s, "test10btrue");
508 /// ```
509 #[macro_export]
510 macro_rules! concat( ($($e:expr),*) => ({ /* compiler built-in */ }) )
511
512 /// A macro which expands to the line number on which it was invoked.
513 ///
514 /// The expanded expression has type `uint`, and the returned line is not
515 /// the invocation of the `line!()` macro itself, but rather the first macro
516 /// invocation leading up to the invocation of the `line!()` macro.
517 ///
518 /// # Example
519 ///
520 /// ```
521 /// let current_line = line!();
522 /// println!("defined on line: {}", current_line);
523 /// ```
524 #[macro_export]
525 macro_rules! line( () => ({ /* compiler built-in */ }) )
526
527 /// A macro which expands to the column number on which it was invoked.
528 ///
529 /// The expanded expression has type `uint`, and the returned column is not
530 /// the invocation of the `col!()` macro itself, but rather the first macro
531 /// invocation leading up to the invocation of the `col!()` macro.
532 ///
533 /// # Example
534 ///
535 /// ```
536 /// let current_col = col!();
537 /// println!("defined on column: {}", current_col);
538 /// ```
539 #[macro_export]
540 macro_rules! col( () => ({ /* compiler built-in */ }) )
541
542 /// A macro which expands to the file name from which it was invoked.
543 ///
544 /// The expanded expression has type `&'static str`, and the returned file
545 /// is not the invocation of the `file!()` macro itself, but rather the
546 /// first macro invocation leading up to the invocation of the `file!()`
547 /// macro.
548 ///
549 /// # Example
550 ///
551 /// ```
552 /// let this_file = file!();
553 /// println!("defined in file: {}", this_file);
554 /// ```
555 #[macro_export]
556 macro_rules! file( () => ({ /* compiler built-in */ }) )
557
558 /// A macro which stringifies its argument.
559 ///
560 /// This macro will yield an expression of type `&'static str` which is the
561 /// stringification of all the tokens passed to the macro. No restrictions
562 /// are placed on the syntax of the macro invocation itself.
563 ///
564 /// # Example
565 ///
566 /// ```
567 /// let one_plus_one = stringify!(1 + 1);
568 /// assert_eq!(one_plus_one, "1 + 1");
569 /// ```
570 #[macro_export]
571 macro_rules! stringify( ($t:tt) => ({ /* compiler built-in */ }) )
572
573 /// Includes a utf8-encoded file as a string.
574 ///
575 /// This macro will yield an expression of type `&'static str` which is the
576 /// contents of the filename specified. The file is located relative to the
577 /// current file (similarly to how modules are found),
578 ///
579 /// # Example
580 ///
581 /// ```rust,ignore
582 /// let secret_key = include_str!("secret-key.ascii");
583 /// ```
584 #[macro_export]
585 macro_rules! include_str( ($file:expr) => ({ /* compiler built-in */ }) )
586
587 /// Includes a file as a byte slice.
588 ///
589 /// This macro will yield an expression of type `&'static [u8]` which is
590 /// the contents of the filename specified. The file is located relative to
591 /// the current file (similarly to how modules are found),
592 ///
593 /// # Example
594 ///
595 /// ```rust,ignore
596 /// let secret_key = include_bin!("secret-key.bin");
597 /// ```
598 #[macro_export]
599 macro_rules! include_bin( ($file:expr) => ({ /* compiler built-in */ }) )
600
601 /// Expands to a string that represents the current module path.
602 ///
603 /// The current module path can be thought of as the hierarchy of modules
604 /// leading back up to the crate root. The first component of the path
605 /// returned is the name of the crate currently being compiled.
606 ///
607 /// # Example
608 ///
609 /// ```rust
610 /// mod test {
611 /// pub fn foo() {
612 /// assert!(module_path!().ends_with("test"));
613 /// }
614 /// }
615 ///
616 /// test::foo();
617 /// ```
618 #[macro_export]
619 macro_rules! module_path( () => ({ /* compiler built-in */ }) )
620
621 /// Boolean evaluation of configuration flags.
622 ///
623 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
624 /// boolean expression evaluation of configuration flags. This frequently
625 /// leads to less duplicated code.
626 ///
627 /// The syntax given to this macro is the same syntax as the `cfg`
628 /// attribute.
629 ///
630 /// # Example
631 ///
632 /// ```rust
633 /// let my_directory = if cfg!(windows) {
634 /// "windows-specific-directory"
635 /// } else {
636 /// "unix-directory"
637 /// };
638 /// ```
639 #[macro_export]
640 macro_rules! cfg( ($cfg:tt) => ({ /* compiler built-in */ }) )
641 }