1 /// Entry point of thread panic. For details, see `std::macros`.
3 #[cfg_attr(not(stage0), allow_internal_unstable(core_panic, __rust_unstable_column))]
4 #[cfg_attr(stage0, allow_internal_unstable)]
5 #[stable(feature = "core", since = "1.6.0")]
8 panic!("explicit panic")
11 $crate::panicking::panic(&($msg, file!(), line!(), __rust_unstable_column!()))
16 ($fmt:expr, $($arg:tt)+) => ({
17 $crate::panicking::panic_fmt(format_args!($fmt, $($arg)*),
18 &(file!(), line!(), __rust_unstable_column!()))
22 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
24 /// On panic, this macro will print the values of the expressions with their
25 /// debug representations.
27 /// Like [`assert!`], this macro has a second form, where a custom
28 /// panic message can be provided.
30 /// [`PartialEq`]: cmp/trait.PartialEq.html
31 /// [`assert!`]: macro.assert.html
40 /// assert_eq!(a, b, "we are testing addition with {} and {}", a, b);
43 #[stable(feature = "rust1", since = "1.0.0")]
44 macro_rules! assert_eq {
45 ($left:expr, $right:expr) => ({
46 match (&$left, &$right) {
47 (left_val, right_val) => {
48 if !(*left_val == *right_val) {
49 // The reborrows below are intentional. Without them, the stack slot for the
50 // borrow is initialized even before the values are compared, leading to a
51 // noticeable slow down.
52 panic!(r#"assertion failed: `(left == right)`
54 right: `{:?}`"#, &*left_val, &*right_val)
59 ($left:expr, $right:expr,) => ({
60 assert_eq!($left, $right)
62 ($left:expr, $right:expr, $($arg:tt)+) => ({
63 match (&($left), &($right)) {
64 (left_val, right_val) => {
65 if !(*left_val == *right_val) {
66 // The reborrows below are intentional. Without them, the stack slot for the
67 // borrow is initialized even before the values are compared, leading to a
68 // noticeable slow down.
69 panic!(r#"assertion failed: `(left == right)`
71 right: `{:?}`: {}"#, &*left_val, &*right_val,
72 format_args!($($arg)+))
79 /// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
81 /// On panic, this macro will print the values of the expressions with their
82 /// debug representations.
84 /// Like [`assert!`], this macro has a second form, where a custom
85 /// panic message can be provided.
87 /// [`PartialEq`]: cmp/trait.PartialEq.html
88 /// [`assert!`]: macro.assert.html
97 /// assert_ne!(a, b, "we are testing that the values are not equal");
100 #[stable(feature = "assert_ne", since = "1.13.0")]
101 macro_rules! assert_ne {
102 ($left:expr, $right:expr) => ({
103 match (&$left, &$right) {
104 (left_val, right_val) => {
105 if *left_val == *right_val {
106 // The reborrows below are intentional. Without them, the stack slot for the
107 // borrow is initialized even before the values are compared, leading to a
108 // noticeable slow down.
109 panic!(r#"assertion failed: `(left != right)`
111 right: `{:?}`"#, &*left_val, &*right_val)
116 ($left:expr, $right:expr,) => {
117 assert_ne!($left, $right)
119 ($left:expr, $right:expr, $($arg:tt)+) => ({
120 match (&($left), &($right)) {
121 (left_val, right_val) => {
122 if *left_val == *right_val {
123 // The reborrows below are intentional. Without them, the stack slot for the
124 // borrow is initialized even before the values are compared, leading to a
125 // noticeable slow down.
126 panic!(r#"assertion failed: `(left != right)`
128 right: `{:?}`: {}"#, &*left_val, &*right_val,
129 format_args!($($arg)+))
136 /// Ensure that a boolean expression is `true` at runtime.
138 /// This will invoke the [`panic!`] macro if the provided expression cannot be
139 /// evaluated to `true` at runtime.
141 /// Like [`assert!`], this macro also has a second version, where a custom panic
142 /// message can be provided.
146 /// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
147 /// optimized builds by default. An optimized build will omit all
148 /// `debug_assert!` statements unless `-C debug-assertions` is passed to the
149 /// compiler. This makes `debug_assert!` useful for checks that are too
150 /// expensive to be present in a release build but may be helpful during
153 /// An unchecked assertion allows a program in an inconsistent state to keep
154 /// running, which might have unexpected consequences but does not introduce
155 /// unsafety as long as this only happens in safe code. The performance cost
156 /// of assertions, is however, not measurable in general. Replacing [`assert!`]
157 /// with `debug_assert!` is thus only encouraged after thorough profiling, and
158 /// more importantly, only in safe code!
160 /// [`panic!`]: macro.panic.html
161 /// [`assert!`]: macro.assert.html
166 /// // the panic message for these assertions is the stringified value of the
167 /// // expression given.
168 /// debug_assert!(true);
170 /// fn some_expensive_computation() -> bool { true } // a very simple function
171 /// debug_assert!(some_expensive_computation());
173 /// // assert with a custom message
175 /// debug_assert!(x, "x wasn't true!");
177 /// let a = 3; let b = 27;
178 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
181 #[stable(feature = "rust1", since = "1.0.0")]
182 macro_rules! debug_assert {
183 ($($arg:tt)*) => (if cfg!(debug_assertions) { assert!($($arg)*); })
186 /// Asserts that two expressions are equal to each other.
188 /// On panic, this macro will print the values of the expressions with their
189 /// debug representations.
191 /// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
192 /// optimized builds by default. An optimized build will omit all
193 /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
194 /// compiler. This makes `debug_assert_eq!` useful for checks that are too
195 /// expensive to be present in a release build but may be helpful during
198 /// [`assert_eq!`]: ../std/macro.assert_eq.html
205 /// debug_assert_eq!(a, b);
208 #[stable(feature = "rust1", since = "1.0.0")]
209 macro_rules! debug_assert_eq {
210 ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_eq!($($arg)*); })
213 /// Asserts that two expressions are not equal to each other.
215 /// On panic, this macro will print the values of the expressions with their
216 /// debug representations.
218 /// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
219 /// optimized builds by default. An optimized build will omit all
220 /// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
221 /// compiler. This makes `debug_assert_ne!` useful for checks that are too
222 /// expensive to be present in a release build but may be helpful during
225 /// [`assert_ne!`]: ../std/macro.assert_ne.html
232 /// debug_assert_ne!(a, b);
235 #[stable(feature = "assert_ne", since = "1.13.0")]
236 macro_rules! debug_assert_ne {
237 ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_ne!($($arg)*); })
240 /// Helper macro for reducing boilerplate code for matching `Result` together
241 /// with converting downstream errors.
243 /// The `?` operator was added to replace `try!` and should be used instead.
244 /// Furthermore, `try` is a reserved word in Rust 2018, so if you must use
245 /// it, you will need to use the [raw-identifier syntax][ris]: `r#try`.
247 /// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
249 /// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
250 /// expression has the value of the wrapped value.
252 /// In case of the `Err` variant, it retrieves the inner error. `try!` then
253 /// performs conversion using `From`. This provides automatic conversion
254 /// between specialized errors and more general ones. The resulting
255 /// error is then immediately returned.
257 /// Because of the early return, `try!` can only be used in functions that
258 /// return [`Result`].
260 /// [`Result`]: ../std/result/enum.Result.html
266 /// use std::fs::File;
267 /// use std::io::prelude::*;
273 /// impl From<io::Error> for MyError {
274 /// fn from(e: io::Error) -> MyError {
275 /// MyError::FileWriteError
279 /// // The preferred method of quick returning Errors
280 /// fn write_to_file_question() -> Result<(), MyError> {
281 /// let mut file = File::create("my_best_friends.txt")?;
282 /// file.write_all(b"This is a list of my best friends.")?;
286 /// // The previous method of quick returning Errors
287 /// fn write_to_file_using_try() -> Result<(), MyError> {
288 /// let mut file = r#try!(File::create("my_best_friends.txt"));
289 /// r#try!(file.write_all(b"This is a list of my best friends."));
293 /// // This is equivalent to:
294 /// fn write_to_file_using_match() -> Result<(), MyError> {
295 /// let mut file = r#try!(File::create("my_best_friends.txt"));
296 /// match file.write_all(b"This is a list of my best friends.") {
298 /// Err(e) => return Err(From::from(e)),
304 #[stable(feature = "rust1", since = "1.0.0")]
307 ($expr:expr) => (match $expr {
308 $crate::result::Result::Ok(val) => val,
309 $crate::result::Result::Err(err) => {
310 return $crate::result::Result::Err($crate::convert::From::from(err))
313 ($expr:expr,) => (r#try!($expr));
316 /// Write formatted data into a buffer.
318 /// This macro accepts a format string, a list of arguments, and a 'writer'. Arguments will be
319 /// formatted according to the specified format string and the result will be passed to the writer.
320 /// The writer may be any value with a `write_fmt` method; generally this comes from an
321 /// implementation of either the [`std::fmt::Write`] or the [`std::io::Write`] trait. The macro
322 /// returns whatever the `write_fmt` method returns; commonly a [`std::fmt::Result`], or an
325 /// See [`std::fmt`] for more information on the format string syntax.
327 /// [`std::fmt`]: ../std/fmt/index.html
328 /// [`std::fmt::Write`]: ../std/fmt/trait.Write.html
329 /// [`std::io::Write`]: ../std/io/trait.Write.html
330 /// [`std::fmt::Result`]: ../std/fmt/type.Result.html
331 /// [`io::Result`]: ../std/io/type.Result.html
336 /// use std::io::Write;
338 /// let mut w = Vec::new();
339 /// write!(&mut w, "test").unwrap();
340 /// write!(&mut w, "formatted {}", "arguments").unwrap();
342 /// assert_eq!(w, b"testformatted arguments");
345 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
346 /// implementing either, as objects do not typically implement both. However, the module must
347 /// import the traits qualified so their names do not conflict:
350 /// use std::fmt::Write as FmtWrite;
351 /// use std::io::Write as IoWrite;
353 /// let mut s = String::new();
354 /// let mut v = Vec::new();
355 /// write!(&mut s, "{} {}", "abc", 123).unwrap(); // uses fmt::Write::write_fmt
356 /// write!(&mut v, "s = {:?}", s).unwrap(); // uses io::Write::write_fmt
357 /// assert_eq!(v, b"s = \"abc 123\"");
360 /// Note: This macro can be used in `no_std` setups as well.
361 /// In a `no_std` setup you are responsible for the implementation details of the components.
364 /// # extern crate core;
365 /// use core::fmt::Write;
369 /// impl Write for Example {
370 /// fn write_str(&mut self, _s: &str) -> core::fmt::Result {
371 /// unimplemented!();
375 /// let mut m = Example{};
376 /// write!(&mut m, "Hello World").expect("Not written");
379 #[stable(feature = "rust1", since = "1.0.0")]
381 ($dst:expr, $($arg:tt)*) => ($dst.write_fmt(format_args!($($arg)*)))
384 /// Write formatted data into a buffer, with a newline appended.
386 /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
387 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
389 /// For more information, see [`write!`]. For information on the format string syntax, see
392 /// [`write!`]: macro.write.html
393 /// [`std::fmt`]: ../std/fmt/index.html
399 /// use std::io::Write;
401 /// let mut w = Vec::new();
402 /// writeln!(&mut w).unwrap();
403 /// writeln!(&mut w, "test").unwrap();
404 /// writeln!(&mut w, "formatted {}", "arguments").unwrap();
406 /// assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
409 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
410 /// implementing either, as objects do not typically implement both. However, the module must
411 /// import the traits qualified so their names do not conflict:
414 /// use std::fmt::Write as FmtWrite;
415 /// use std::io::Write as IoWrite;
417 /// let mut s = String::new();
418 /// let mut v = Vec::new();
419 /// writeln!(&mut s, "{} {}", "abc", 123).unwrap(); // uses fmt::Write::write_fmt
420 /// writeln!(&mut v, "s = {:?}", s).unwrap(); // uses io::Write::write_fmt
421 /// assert_eq!(v, b"s = \"abc 123\\n\"\n");
424 #[stable(feature = "rust1", since = "1.0.0")]
425 #[cfg_attr(stage0, allow_internal_unstable)]
426 #[cfg_attr(not(stage0), allow_internal_unstable(format_args_nl))]
427 macro_rules! writeln {
434 ($dst:expr, $($arg:tt)*) => (
435 $dst.write_fmt(format_args_nl!($($arg)*))
439 /// A utility macro for indicating unreachable code.
441 /// This is useful any time that the compiler can't determine that some code is unreachable. For
444 /// * Match arms with guard conditions.
445 /// * Loops that dynamically terminate.
446 /// * Iterators that dynamically terminate.
448 /// If the determination that the code is unreachable proves incorrect, the
449 /// program immediately terminates with a [`panic!`]. The function [`unreachable_unchecked`],
450 /// which belongs to the [`std::hint`] module, informs the compiler to
451 /// optimize the code out of the release version entirely.
453 /// [`panic!`]: ../std/macro.panic.html
454 /// [`unreachable_unchecked`]: ../std/hint/fn.unreachable_unchecked.html
455 /// [`std::hint`]: ../std/hint/index.html
459 /// This will always [`panic!`]
461 /// [`panic!`]: ../std/macro.panic.html
467 /// # #[allow(dead_code)]
468 /// fn foo(x: Option<i32>) {
470 /// Some(n) if n >= 0 => println!("Some(Non-negative)"),
471 /// Some(n) if n < 0 => println!("Some(Negative)"),
472 /// Some(_) => unreachable!(), // compile error if commented out
473 /// None => println!("None")
481 /// # #[allow(dead_code)]
482 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
484 /// if 3*i < i { panic!("u32 overflow"); }
485 /// if x < 3*i { return i-1; }
491 #[stable(feature = "rust1", since = "1.0.0")]
492 macro_rules! unreachable {
494 panic!("internal error: entered unreachable code")
497 unreachable!("{}", $msg)
502 ($fmt:expr, $($arg:tt)*) => ({
503 panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
507 /// A standardized placeholder for marking unfinished code.
509 /// This can be useful if you are prototyping and are just looking to have your
510 /// code type-check, or if you're implementing a trait that requires multiple
511 /// methods, and you're only planning on using one of them.
515 /// This will always [panic!](macro.panic.html)
519 /// Here's an example of some in-progress code. We have a trait `Foo`:
528 /// We want to implement `Foo` on one of our types, but we also want to work on
529 /// just `bar()` first. In order for our code to compile, we need to implement
530 /// `baz()`, so we can use `unimplemented!`:
539 /// impl Foo for MyStruct {
541 /// // implementation goes here
545 /// // let's not worry about implementing baz() for now
546 /// unimplemented!();
551 /// let s = MyStruct;
554 /// // we aren't even using baz() yet, so this is fine.
558 #[stable(feature = "rust1", since = "1.0.0")]
559 macro_rules! unimplemented {
560 () => (panic!("not yet implemented"));
561 ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*)));
564 /// A macro to create an array of [`MaybeUninit`]
566 /// This macro constructs an uninitialized array of the type `[MaybeUninit<K>; N]`.
568 /// [`MaybeUninit`]: mem/union.MaybeUninit.html
570 #[unstable(feature = "maybe_uninit_array", issue = "53491")]
571 macro_rules! uninitialized_array {
572 // This `into_initialized` is safe because an array of `MaybeUninit` does not
573 // require initialization.
574 // FIXME(#49147): Could be replaced by an array initializer, once those can
575 // be any const expression.
576 ($t:ty; $size:expr) => (unsafe {
577 MaybeUninit::<[MaybeUninit<$t>; $size]>::uninitialized().into_initialized()
581 /// Built-in macros to the compiler itself.
583 /// These macros do not have any corresponding definition with a `macro_rules!`
584 /// macro, but are documented here. Their implementations can be found hardcoded
585 /// into libsyntax itself.
587 /// For more information, see documentation for `std`'s macros.
591 /// Unconditionally causes compilation to fail with the given error message when encountered.
593 /// For more information, see the documentation for [`std::compile_error!`].
595 /// [`std::compile_error!`]: ../std/macro.compile_error.html
596 #[stable(feature = "compile_error_macro", since = "1.20.0")]
597 #[rustc_doc_only_macro]
598 macro_rules! compile_error {
599 ($msg:expr) => ({ /* compiler built-in */ });
600 ($msg:expr,) => ({ /* compiler built-in */ });
603 /// The core macro for formatted string creation & output.
605 /// For more information, see the documentation for [`std::format_args!`].
607 /// [`std::format_args!`]: ../std/macro.format_args.html
608 #[stable(feature = "rust1", since = "1.0.0")]
609 #[rustc_doc_only_macro]
610 macro_rules! format_args {
611 ($fmt:expr) => ({ /* compiler built-in */ });
612 ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ });
615 /// Inspect an environment variable at compile time.
617 /// For more information, see the documentation for [`std::env!`].
619 /// [`std::env!`]: ../std/macro.env.html
620 #[stable(feature = "rust1", since = "1.0.0")]
621 #[rustc_doc_only_macro]
623 ($name:expr) => ({ /* compiler built-in */ });
624 ($name:expr,) => ({ /* compiler built-in */ });
627 /// Optionally inspect an environment variable at compile time.
629 /// For more information, see the documentation for [`std::option_env!`].
631 /// [`std::option_env!`]: ../std/macro.option_env.html
632 #[stable(feature = "rust1", since = "1.0.0")]
633 #[rustc_doc_only_macro]
634 macro_rules! option_env {
635 ($name:expr) => ({ /* compiler built-in */ });
636 ($name:expr,) => ({ /* compiler built-in */ });
639 /// Concatenate identifiers into one identifier.
641 /// For more information, see the documentation for [`std::concat_idents!`].
643 /// [`std::concat_idents!`]: ../std/macro.concat_idents.html
644 #[unstable(feature = "concat_idents_macro", issue = "29599")]
645 #[rustc_doc_only_macro]
646 macro_rules! concat_idents {
647 ($($e:ident),+) => ({ /* compiler built-in */ });
648 ($($e:ident,)+) => ({ /* compiler built-in */ });
651 /// Concatenates literals into a static string slice.
653 /// For more information, see the documentation for [`std::concat!`].
655 /// [`std::concat!`]: ../std/macro.concat.html
656 #[stable(feature = "rust1", since = "1.0.0")]
657 #[rustc_doc_only_macro]
658 macro_rules! concat {
659 ($($e:expr),*) => ({ /* compiler built-in */ });
660 ($($e:expr,)*) => ({ /* compiler built-in */ });
663 /// A macro which expands to the line number on which it was invoked.
665 /// For more information, see the documentation for [`std::line!`].
667 /// [`std::line!`]: ../std/macro.line.html
668 #[stable(feature = "rust1", since = "1.0.0")]
669 #[rustc_doc_only_macro]
670 macro_rules! line { () => ({ /* compiler built-in */ }) }
672 /// A macro which expands to the column number on which it was invoked.
674 /// For more information, see the documentation for [`std::column!`].
676 /// [`std::column!`]: ../std/macro.column.html
677 #[stable(feature = "rust1", since = "1.0.0")]
678 #[rustc_doc_only_macro]
679 macro_rules! column { () => ({ /* compiler built-in */ }) }
681 /// A macro which expands to the file name from which it was invoked.
683 /// For more information, see the documentation for [`std::file!`].
685 /// [`std::file!`]: ../std/macro.file.html
686 #[stable(feature = "rust1", since = "1.0.0")]
687 #[rustc_doc_only_macro]
688 macro_rules! file { () => ({ /* compiler built-in */ }) }
690 /// A macro which stringifies its arguments.
692 /// For more information, see the documentation for [`std::stringify!`].
694 /// [`std::stringify!`]: ../std/macro.stringify.html
695 #[stable(feature = "rust1", since = "1.0.0")]
696 #[rustc_doc_only_macro]
697 macro_rules! stringify { ($($t:tt)*) => ({ /* compiler built-in */ }) }
699 /// Includes a utf8-encoded file as a string.
701 /// For more information, see the documentation for [`std::include_str!`].
703 /// [`std::include_str!`]: ../std/macro.include_str.html
704 #[stable(feature = "rust1", since = "1.0.0")]
705 #[rustc_doc_only_macro]
706 macro_rules! include_str {
707 ($file:expr) => ({ /* compiler built-in */ });
708 ($file:expr,) => ({ /* compiler built-in */ });
711 /// Includes a file as a reference to a byte array.
713 /// For more information, see the documentation for [`std::include_bytes!`].
715 /// [`std::include_bytes!`]: ../std/macro.include_bytes.html
716 #[stable(feature = "rust1", since = "1.0.0")]
717 #[rustc_doc_only_macro]
718 macro_rules! include_bytes {
719 ($file:expr) => ({ /* compiler built-in */ });
720 ($file:expr,) => ({ /* compiler built-in */ });
723 /// Expands to a string that represents the current module path.
725 /// For more information, see the documentation for [`std::module_path!`].
727 /// [`std::module_path!`]: ../std/macro.module_path.html
728 #[stable(feature = "rust1", since = "1.0.0")]
729 #[rustc_doc_only_macro]
730 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
732 /// Boolean evaluation of configuration flags, at compile-time.
734 /// For more information, see the documentation for [`std::cfg!`].
736 /// [`std::cfg!`]: ../std/macro.cfg.html
737 #[stable(feature = "rust1", since = "1.0.0")]
738 #[rustc_doc_only_macro]
739 macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
741 /// Parse a file as an expression or an item according to the context.
743 /// For more information, see the documentation for [`std::include!`].
745 /// [`std::include!`]: ../std/macro.include.html
746 #[stable(feature = "rust1", since = "1.0.0")]
747 #[rustc_doc_only_macro]
748 macro_rules! include {
749 ($file:expr) => ({ /* compiler built-in */ });
750 ($file:expr,) => ({ /* compiler built-in */ });
753 /// Ensure that a boolean expression is `true` at runtime.
755 /// For more information, see the documentation for [`std::assert!`].
757 /// [`std::assert!`]: ../std/macro.assert.html
758 #[rustc_doc_only_macro]
759 #[stable(feature = "rust1", since = "1.0.0")]
760 macro_rules! assert {
761 ($cond:expr) => ({ /* compiler built-in */ });
762 ($cond:expr,) => ({ /* compiler built-in */ });
763 ($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ });