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 ($left:expr , $right:expr) => ({
124 match (&($left), &($right)) {
125 (left_val, right_val) => {
126 // check both directions of equality....
127 if !((*left_val == *right_val) &&
128 (*right_val == *left_val)) {
129 panic!("assertion failed: `(left == right) && (right == left)` \
130 (left: `{}`, right: `{}`)", *left_val, *right_val)
137 /// Ensure that a boolean expression is `true` at runtime.
139 /// This will invoke the `panic!` macro if the provided expression cannot be
140 /// evaluated to `true` at runtime.
142 /// Unlike `assert!`, `debug_assert!` statements can be disabled by passing
143 /// `--cfg ndebug` to the compiler. This makes `debug_assert!` useful for
144 /// checks that are too expensive to be present in a release build but may be
145 /// helpful during development.
150 /// // the panic message for these assertions is the stringified value of the
151 /// // expression given.
152 /// debug_assert!(true);
153 /// # fn some_expensive_computation() -> bool { true }
154 /// debug_assert!(some_expensive_computation());
156 /// // assert with a custom message
158 /// debug_assert!(x, "x wasn't true!");
159 /// # let a = 3i; let b = 27i;
160 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
163 macro_rules! debug_assert {
164 ($($arg:tt)*) => (if cfg!(not(ndebug)) { assert!($($arg)*); })
167 /// Asserts that two expressions are equal to each other, testing equality in
170 /// On panic, this macro will print the values of the expressions.
172 /// Unlike `assert_eq!`, `debug_assert_eq!` statements can be disabled by
173 /// passing `--cfg ndebug` to the compiler. This makes `debug_assert_eq!`
174 /// useful for checks that are too expensive to be present in a release build
175 /// but may be helpful during development.
182 /// debug_assert_eq!(a, b);
185 macro_rules! debug_assert_eq {
186 ($($arg:tt)*) => (if cfg!(not(ndebug)) { assert_eq!($($arg)*); })
189 /// A utility macro for indicating unreachable code.
191 /// This is useful any time that the compiler can't determine that some code is unreachable. For
194 /// * Match arms with guard conditions.
195 /// * Loops that dynamically terminate.
196 /// * Iterators that dynamically terminate.
200 /// This will always panic.
207 /// fn foo(x: Option<int>) {
209 /// Some(n) if n >= 0 => println!("Some(Non-negative)"),
210 /// Some(n) if n < 0 => println!("Some(Negative)"),
211 /// Some(_) => unreachable!(), // compile error if commented out
212 /// None => println!("None")
220 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
221 /// for i in std::iter::count(0_u32, 1) {
222 /// if 3*i < i { panic!("u32 overflow"); }
223 /// if x < 3*i { return i-1; }
229 macro_rules! unreachable {
231 panic!("internal error: entered unreachable code")
234 unreachable!("{}", $msg)
236 ($fmt:expr, $($arg:tt)*) => ({
237 panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
241 /// A standardised placeholder for marking unfinished code. It panics with the
242 /// message `"not yet implemented"` when executed.
244 macro_rules! unimplemented {
245 () => (panic!("not yet implemented"))
248 /// Use the syntax described in `std::fmt` to create a value of type `String`.
249 /// See `std::fmt` for more information.
255 /// format!("hello {}", "world!");
256 /// format!("x = {}, y = {y}", 10i, y = 30i);
260 macro_rules! format {
262 format_args!(::std::fmt::format, $($arg)*)
266 /// Use the `format!` syntax to write data into a buffer of type `&mut Writer`.
267 /// See `std::fmt` for more information.
272 /// # #![allow(unused_must_use)]
274 /// let mut w = Vec::new();
275 /// write!(&mut w, "test");
276 /// write!(&mut w, "formatted {}", "arguments");
281 ($dst:expr, $($arg:tt)*) => ({
282 let dst = &mut *$dst;
283 format_args!(|args| { dst.write_fmt(args) }, $($arg)*)
287 /// Equivalent to the `write!` macro, except that a newline is appended after
288 /// the message is written.
291 macro_rules! writeln {
292 ($dst:expr, $fmt:expr $($arg:tt)*) => (
293 write!($dst, concat!($fmt, "\n") $($arg)*)
297 /// Equivalent to the `println!` macro except that a newline is not printed at
298 /// the end of the message.
302 ($($arg:tt)*) => (format_args!(::std::io::stdio::print_args, $($arg)*))
305 /// Macro for printing to a task's stdout handle.
307 /// Each task can override its stdout handle via `std::io::stdio::set_stdout`.
308 /// The syntax of this macro is the same as that used for `format!`. For more
309 /// information, see `std::fmt` and `std::io::stdio`.
314 /// println!("hello there!");
315 /// println!("format {} arguments", "some");
319 macro_rules! println {
320 ($($arg:tt)*) => (format_args!(::std::io::stdio::println_args, $($arg)*))
323 /// Helper macro for unwrapping `Result` values while returning early with an
324 /// error if the value of the expression is `Err`. For more information, see
331 Err(err) => return Err(::std::error::FromError::from_error(err))
336 /// Create a `std::vec::Vec` containing the arguments.
340 use std::slice::BoxedSliceExt;
341 let xs: ::std::boxed::Box<[_]> = box [$($x),*];
344 ($($x:expr,)*) => (vec![$($x),*])
347 /// A macro to select an event from a number of receivers.
349 /// This macro is used to wait for the first event to occur on a number of
350 /// receivers. It places no restrictions on the types of receivers given to
351 /// this macro, this can be viewed as a heterogeneous select.
356 /// use std::thread::Thread;
358 /// let (tx1, rx1) = channel();
359 /// let (tx2, rx2) = channel();
360 /// # fn long_running_task() {}
361 /// # fn calculate_the_answer() -> int { 42i }
363 /// Thread::spawn(move|| { long_running_task(); tx1.send(()) }).detach();
364 /// Thread::spawn(move|| { tx2.send(calculate_the_answer()) }).detach();
367 /// () = rx1.recv() => println!("the long running task finished first"),
368 /// answer = rx2.recv() => {
369 /// println!("the answer was: {}", answer);
374 /// For more information about select, see the `std::comm::Select` structure.
377 macro_rules! select {
379 $($name:pat = $rx:ident.$meth:ident() => $code:expr),+
381 use std::comm::Select;
382 let sel = Select::new();
383 $( let mut $rx = sel.handle(&$rx); )+
387 let ret = sel.wait();
388 $( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
393 // When testing the standard library, we link to the liblog crate to get the
394 // logging macros. In doing so, the liblog crate was linked against the real
395 // version of libstd, and uses a different std::fmt module than the test crate
396 // uses. To get around this difference, we redefine the log!() macro here to be
397 // just a dumb version of what it should be.
400 ($lvl:expr, $($args:tt)*) => (
401 if log_enabled!($lvl) { println!($($args)*) }
405 /// Built-in macros to the compiler itself.
407 /// These macros do not have any corresponding definition with a `macro_rules!`
408 /// macro, but are documented here. Their implementations can be found hardcoded
409 /// into libsyntax itself.
412 /// The core macro for formatted string creation & output.
414 /// This macro takes as its first argument a callable expression which will
415 /// receive as its first argument a value of type `&fmt::Arguments`. This
416 /// value can be passed to the functions in `std::fmt` for performing useful
417 /// functions. All other formatting macros (`format!`, `write!`,
418 /// `println!`, etc) are proxied through this one.
420 /// For more information, see the documentation in `std::fmt`.
427 /// let s = format_args!(fmt::format, "hello {}", "world");
428 /// assert_eq!(s, format!("hello {}", "world"));
430 /// format_args!(|args| {
431 /// // pass `args` to another function, etc.
432 /// }, "hello {}", "world");
435 macro_rules! format_args { ($closure:expr, $fmt:expr $($args:tt)*) => ({
436 /* compiler built-in */
439 /// Inspect an environment variable at compile time.
441 /// This macro will expand to the value of the named environment variable at
442 /// compile time, yielding an expression of type `&'static str`.
444 /// If the environment variable is not defined, then a compilation error
445 /// will be emitted. To not emit a compile error, use the `option_env!`
451 /// let path: &'static str = env!("PATH");
452 /// println!("the $PATH variable at the time of compiling was: {}", path);
455 macro_rules! env { ($name:expr) => ({ /* compiler built-in */ }) }
457 /// Optionally inspect an environment variable at compile time.
459 /// If the named environment variable is present at compile time, this will
460 /// expand into an expression of type `Option<&'static str>` whose value is
461 /// `Some` of the value of the environment variable. If the environment
462 /// variable is not present, then this will expand to `None`.
464 /// A compile time error is never emitted when using this macro regardless
465 /// of whether the environment variable is present or not.
470 /// let key: Option<&'static str> = option_env!("SECRET_KEY");
471 /// println!("the secret key might be: {}", key);
474 macro_rules! option_env { ($name:expr) => ({ /* compiler built-in */ }) }
476 /// Concatenate literals into a static byte slice.
478 /// This macro takes any number of comma-separated literal expressions,
479 /// yielding an expression of type `&'static [u8]` which is the
480 /// concatenation (left to right) of all the literals in their byte format.
482 /// This extension currently only supports string literals, character
483 /// literals, and integers less than 256. The byte slice returned is the
484 /// utf8-encoding of strings and characters.
489 /// let rust = bytes!("r", 'u', "st", 255);
490 /// assert_eq!(rust[1], b'u');
491 /// assert_eq!(rust[4], 255);
494 macro_rules! bytes { ($($e:expr),*) => ({ /* compiler built-in */ }) }
496 /// Concatenate identifiers into one identifier.
498 /// This macro takes any number of comma-separated identifiers, and
499 /// concatenates them all into one, yielding an expression which is a new
500 /// identifier. Note that hygiene makes it such that this macro cannot
501 /// capture local variables, and macros are only allowed in item,
502 /// statement or expression position, meaning this macro may be difficult to
503 /// use in some situations.
508 /// #![feature(concat_idents)]
511 /// fn foobar() -> int { 23 }
513 /// let f = concat_idents!(foo, bar);
514 /// println!("{}", f());
518 macro_rules! concat_idents {
519 ($($e:ident),*) => ({ /* compiler built-in */ })
522 /// Concatenates literals into a static string slice.
524 /// This macro takes any number of comma-separated literals, yielding an
525 /// expression of type `&'static str` which represents all of the literals
526 /// concatenated left-to-right.
528 /// Integer and floating point literals are stringified in order to be
534 /// let s = concat!("test", 10i, 'b', true);
535 /// assert_eq!(s, "test10btrue");
538 macro_rules! concat { ($($e:expr),*) => ({ /* compiler built-in */ }) }
540 /// A macro which expands to the line number on which it was invoked.
542 /// The expanded expression has type `uint`, and the returned line is not
543 /// the invocation of the `line!()` macro itself, but rather the first macro
544 /// invocation leading up to the invocation of the `line!()` macro.
549 /// let current_line = line!();
550 /// println!("defined on line: {}", current_line);
553 macro_rules! line { () => ({ /* compiler built-in */ }) }
555 /// A macro which expands to the column number on which it was invoked.
557 /// The expanded expression has type `uint`, and the returned column is not
558 /// the invocation of the `column!()` macro itself, but rather the first macro
559 /// invocation leading up to the invocation of the `column!()` macro.
564 /// let current_col = column!();
565 /// println!("defined on column: {}", current_col);
568 macro_rules! column { () => ({ /* compiler built-in */ }) }
570 /// A macro which expands to the file name from which it was invoked.
572 /// The expanded expression has type `&'static str`, and the returned file
573 /// is not the invocation of the `file!()` macro itself, but rather the
574 /// first macro invocation leading up to the invocation of the `file!()`
580 /// let this_file = file!();
581 /// println!("defined in file: {}", this_file);
584 macro_rules! file { () => ({ /* compiler built-in */ }) }
586 /// A macro which stringifies its argument.
588 /// This macro will yield an expression of type `&'static str` which is the
589 /// stringification of all the tokens passed to the macro. No restrictions
590 /// are placed on the syntax of the macro invocation itself.
595 /// let one_plus_one = stringify!(1 + 1);
596 /// assert_eq!(one_plus_one, "1 + 1");
599 macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
601 /// Includes a utf8-encoded file as a string.
603 /// This macro will yield an expression of type `&'static str` which is the
604 /// contents of the filename specified. The file is located relative to the
605 /// current file (similarly to how modules are found),
610 /// let secret_key = include_str!("secret-key.ascii");
613 macro_rules! include_str { ($file:expr) => ({ /* compiler built-in */ }) }
615 /// Includes a file as a byte slice.
617 /// This macro will yield an expression of type `&'static [u8]` which is
618 /// the contents of the filename specified. The file is located relative to
619 /// the current file (similarly to how modules are found),
624 /// let secret_key = include_bytes!("secret-key.bin");
627 macro_rules! include_bytes { ($file:expr) => ({ /* compiler built-in */ }) }
629 /// Deprecated alias for `include_bytes!()`.
631 macro_rules! include_bin { ($file:expr) => ({ /* compiler built-in */}) }
633 /// Expands to a string that represents the current module path.
635 /// The current module path can be thought of as the hierarchy of modules
636 /// leading back up to the crate root. The first component of the path
637 /// returned is the name of the crate currently being compiled.
644 /// assert!(module_path!().ends_with("test"));
651 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
653 /// Boolean evaluation of configuration flags.
655 /// In addition to the `#[cfg]` attribute, this macro is provided to allow
656 /// boolean expression evaluation of configuration flags. This frequently
657 /// leads to less duplicated code.
659 /// The syntax given to this macro is the same syntax as the `cfg`
665 /// let my_directory = if cfg!(windows) {
666 /// "windows-specific-directory"
672 macro_rules! cfg { ($cfg:tt) => ({ /* compiler built-in */ }) }