1 /// Panics the current thread.
3 /// For details, see `std::macros`.
5 #[allow_internal_unstable(core_panic, __rust_unstable_column)]
6 #[stable(feature = "core", since = "1.6.0")]
9 panic!("explicit panic")
12 $crate::panicking::panic(&($msg, file!(), line!(), __rust_unstable_column!()))
17 ($fmt:expr, $($arg:tt)+) => ({
18 $crate::panicking::panic_fmt(format_args!($fmt, $($arg)*),
19 &(file!(), line!(), __rust_unstable_column!()))
23 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).
25 /// On panic, this macro will print the values of the expressions with their
26 /// debug representations.
28 /// Like [`assert!`], this macro has a second form, where a custom
29 /// panic message can be provided.
31 /// [`PartialEq`]: cmp/trait.PartialEq.html
32 /// [`assert!`]: macro.assert.html
41 /// assert_eq!(a, b, "we are testing addition with {} and {}", a, b);
44 #[stable(feature = "rust1", since = "1.0.0")]
45 macro_rules! assert_eq {
46 ($left:expr, $right:expr) => ({
47 match (&$left, &$right) {
48 (left_val, right_val) => {
49 if !(*left_val == *right_val) {
50 // The reborrows below are intentional. Without them, the stack slot for the
51 // borrow is initialized even before the values are compared, leading to a
52 // noticeable slow down.
53 panic!(r#"assertion failed: `(left == right)`
55 right: `{:?}`"#, &*left_val, &*right_val)
60 ($left:expr, $right:expr,) => ({
61 assert_eq!($left, $right)
63 ($left:expr, $right:expr, $($arg:tt)+) => ({
64 match (&($left), &($right)) {
65 (left_val, right_val) => {
66 if !(*left_val == *right_val) {
67 // The reborrows below are intentional. Without them, the stack slot for the
68 // borrow is initialized even before the values are compared, leading to a
69 // noticeable slow down.
70 panic!(r#"assertion failed: `(left == right)`
72 right: `{:?}`: {}"#, &*left_val, &*right_val,
73 format_args!($($arg)+))
80 /// Asserts that two expressions are not equal to each other (using [`PartialEq`]).
82 /// On panic, this macro will print the values of the expressions with their
83 /// debug representations.
85 /// Like [`assert!`], this macro has a second form, where a custom
86 /// panic message can be provided.
88 /// [`PartialEq`]: cmp/trait.PartialEq.html
89 /// [`assert!`]: macro.assert.html
98 /// assert_ne!(a, b, "we are testing that the values are not equal");
101 #[stable(feature = "assert_ne", since = "1.13.0")]
102 macro_rules! assert_ne {
103 ($left:expr, $right:expr) => ({
104 match (&$left, &$right) {
105 (left_val, right_val) => {
106 if *left_val == *right_val {
107 // The reborrows below are intentional. Without them, the stack slot for the
108 // borrow is initialized even before the values are compared, leading to a
109 // noticeable slow down.
110 panic!(r#"assertion failed: `(left != right)`
112 right: `{:?}`"#, &*left_val, &*right_val)
117 ($left:expr, $right:expr,) => {
118 assert_ne!($left, $right)
120 ($left:expr, $right:expr, $($arg:tt)+) => ({
121 match (&($left), &($right)) {
122 (left_val, right_val) => {
123 if *left_val == *right_val {
124 // The reborrows below are intentional. Without them, the stack slot for the
125 // borrow is initialized even before the values are compared, leading to a
126 // noticeable slow down.
127 panic!(r#"assertion failed: `(left != right)`
129 right: `{:?}`: {}"#, &*left_val, &*right_val,
130 format_args!($($arg)+))
137 /// Asserts 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 /// Like [`assert!`], this macro also has a second version, where a custom panic
143 /// message can be provided.
147 /// Unlike [`assert!`], `debug_assert!` statements are only enabled in non
148 /// optimized builds by default. An optimized build will omit all
149 /// `debug_assert!` statements unless `-C debug-assertions` is passed to the
150 /// compiler. This makes `debug_assert!` useful for checks that are too
151 /// expensive to be present in a release build but may be helpful during
154 /// An unchecked assertion allows a program in an inconsistent state to keep
155 /// running, which might have unexpected consequences but does not introduce
156 /// unsafety as long as this only happens in safe code. The performance cost
157 /// of assertions, is however, not measurable in general. Replacing [`assert!`]
158 /// with `debug_assert!` is thus only encouraged after thorough profiling, and
159 /// more importantly, only in safe code!
161 /// [`panic!`]: macro.panic.html
162 /// [`assert!`]: macro.assert.html
167 /// // the panic message for these assertions is the stringified value of the
168 /// // expression given.
169 /// debug_assert!(true);
171 /// fn some_expensive_computation() -> bool { true } // a very simple function
172 /// debug_assert!(some_expensive_computation());
174 /// // assert with a custom message
176 /// debug_assert!(x, "x wasn't true!");
178 /// let a = 3; let b = 27;
179 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
182 #[stable(feature = "rust1", since = "1.0.0")]
183 macro_rules! debug_assert {
184 ($($arg:tt)*) => (if cfg!(debug_assertions) { assert!($($arg)*); })
187 /// Asserts that two expressions are equal to each other.
189 /// On panic, this macro will print the values of the expressions with their
190 /// debug representations.
192 /// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
193 /// optimized builds by default. An optimized build will omit all
194 /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
195 /// compiler. This makes `debug_assert_eq!` useful for checks that are too
196 /// expensive to be present in a release build but may be helpful during
199 /// [`assert_eq!`]: ../std/macro.assert_eq.html
206 /// debug_assert_eq!(a, b);
209 #[stable(feature = "rust1", since = "1.0.0")]
210 macro_rules! debug_assert_eq {
211 ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_eq!($($arg)*); })
214 /// Asserts that two expressions are not equal to each other.
216 /// On panic, this macro will print the values of the expressions with their
217 /// debug representations.
219 /// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
220 /// optimized builds by default. An optimized build will omit all
221 /// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
222 /// compiler. This makes `debug_assert_ne!` useful for checks that are too
223 /// expensive to be present in a release build but may be helpful during
226 /// [`assert_ne!`]: ../std/macro.assert_ne.html
233 /// debug_assert_ne!(a, b);
236 #[stable(feature = "assert_ne", since = "1.13.0")]
237 macro_rules! debug_assert_ne {
238 ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_ne!($($arg)*); })
241 /// Unwraps a result or propagates its error.
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 /// Writes 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)*) => ($dst.write_fmt(format_args!($($arg)*)))
384 /// Write formatted data into a buffer, with a newline appended.
386 /// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
387 /// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
389 /// For more information, see [`write!`]. For information on the format string syntax, see
392 /// [`write!`]: macro.write.html
393 /// [`std::fmt`]: ../std/fmt/index.html
399 /// use std::io::Write;
401 /// let mut w = Vec::new();
402 /// writeln!(&mut w).unwrap();
403 /// writeln!(&mut w, "test").unwrap();
404 /// writeln!(&mut w, "formatted {}", "arguments").unwrap();
406 /// assert_eq!(&w[..], "\ntest\nformatted arguments\n".as_bytes());
409 /// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
410 /// implementing either, as objects do not typically implement both. However, the module must
411 /// import the traits qualified so their names do not conflict:
414 /// use std::fmt::Write as FmtWrite;
415 /// use std::io::Write as IoWrite;
417 /// let mut s = String::new();
418 /// let mut v = Vec::new();
419 /// writeln!(&mut s, "{} {}", "abc", 123).unwrap(); // uses fmt::Write::write_fmt
420 /// writeln!(&mut v, "s = {:?}", s).unwrap(); // uses io::Write::write_fmt
421 /// assert_eq!(v, b"s = \"abc 123\\n\"\n");
424 #[stable(feature = "rust1", since = "1.0.0")]
425 #[allow_internal_unstable(format_args_nl)]
426 macro_rules! writeln {
433 ($dst:expr, $($arg:tt)*) => (
434 $dst.write_fmt(format_args_nl!($($arg)*))
438 /// Indicates unreachable code.
440 /// This is useful any time that the compiler can't determine that some code is unreachable. For
443 /// * Match arms with guard conditions.
444 /// * Loops that dynamically terminate.
445 /// * Iterators that dynamically terminate.
447 /// If the determination that the code is unreachable proves incorrect, the
448 /// program immediately terminates with a [`panic!`].
450 /// The unsafe counterpart of this macro is the [`unreachable_unchecked`] function, which
451 /// will cause undefined behavior if the code is reached.
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 /// Indicates 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 /// Indicates unfinished code.
566 /// This can be useful if you are prototyping and are just looking to have your
567 /// code typecheck. `todo!` works exactly like `unimplemented!`. The only
568 /// difference between the two macros is the name.
572 /// This will always [panic!](macro.panic.html)
576 /// Here's an example of some in-progress code. We have a trait `Foo`:
585 /// We want to implement `Foo` on one of our types, but we also want to work on
586 /// just `bar()` first. In order for our code to compile, we need to implement
587 /// `baz()`, so we can use `todo!`:
590 /// #![feature(todo_macro)]
598 /// impl Foo for MyStruct {
600 /// // implementation goes here
604 /// // let's not worry about implementing baz() for now
610 /// let s = MyStruct;
613 /// // we aren't even using baz() yet, so this is fine.
617 #[unstable(feature = "todo_macro", issue = "59277")]
619 () => (panic!("not yet implemented"));
620 ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*)));
623 /// Creates an array of [`MaybeUninit`].
625 /// This macro constructs an uninitialized array of the type `[MaybeUninit<K>; N]`.
627 /// [`MaybeUninit`]: mem/union.MaybeUninit.html
629 #[unstable(feature = "maybe_uninit_array", issue = "53491")]
630 macro_rules! uninitialized_array {
631 // This `assume_init` is safe because an array of `MaybeUninit` does not
632 // require initialization.
633 // FIXME(#49147): Could be replaced by an array initializer, once those can
634 // be any const expression.
635 ($t:ty; $size:expr) => (unsafe {
636 MaybeUninit::<[MaybeUninit<$t>; $size]>::uninit().assume_init()
640 /// Built-in macros to the compiler itself.
642 /// These macros do not have any corresponding definition with a `macro_rules!`
643 /// macro, but are documented here. Their implementations can be found hardcoded
644 /// into libsyntax itself.
646 /// For more information, see documentation for `std`'s macros.
650 /// Causes compilation to fail with the given error message when encountered.
652 /// For more information, see the documentation for [`std::compile_error!`].
654 /// [`std::compile_error!`]: ../std/macro.compile_error.html
655 #[stable(feature = "compile_error_macro", since = "1.20.0")]
656 #[rustc_doc_only_macro]
657 macro_rules! compile_error {
658 ($msg:expr) => ({ /* compiler built-in */ });
659 ($msg:expr,) => ({ /* compiler built-in */ });
662 /// Constructs parameters for the other string-formatting macros.
664 /// For more information, see the documentation for [`std::format_args!`].
666 /// [`std::format_args!`]: ../std/macro.format_args.html
667 #[stable(feature = "rust1", since = "1.0.0")]
668 #[rustc_doc_only_macro]
669 macro_rules! format_args {
670 ($fmt:expr) => ({ /* compiler built-in */ });
671 ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ });
674 /// Inspects an environment variable at compile time.
676 /// For more information, see the documentation for [`std::env!`].
678 /// [`std::env!`]: ../std/macro.env.html
679 #[stable(feature = "rust1", since = "1.0.0")]
680 #[rustc_doc_only_macro]
682 ($name:expr) => ({ /* compiler built-in */ });
683 ($name:expr,) => ({ /* compiler built-in */ });
686 /// Optionally inspects an environment variable at compile time.
688 /// For more information, see the documentation for [`std::option_env!`].
690 /// [`std::option_env!`]: ../std/macro.option_env.html
691 #[stable(feature = "rust1", since = "1.0.0")]
692 #[rustc_doc_only_macro]
693 macro_rules! option_env {
694 ($name:expr) => ({ /* compiler built-in */ });
695 ($name:expr,) => ({ /* compiler built-in */ });
698 /// Concatenates identifiers into one identifier.
700 /// For more information, see the documentation for [`std::concat_idents!`].
702 /// [`std::concat_idents!`]: ../std/macro.concat_idents.html
703 #[unstable(feature = "concat_idents_macro", issue = "29599")]
704 #[rustc_doc_only_macro]
705 macro_rules! concat_idents {
706 ($($e:ident),+) => ({ /* compiler built-in */ });
707 ($($e:ident,)+) => ({ /* compiler built-in */ });
710 /// Concatenates literals into a static string slice.
712 /// For more information, see the documentation for [`std::concat!`].
714 /// [`std::concat!`]: ../std/macro.concat.html
715 #[stable(feature = "rust1", since = "1.0.0")]
716 #[rustc_doc_only_macro]
717 macro_rules! concat {
718 ($($e:expr),*) => ({ /* compiler built-in */ });
719 ($($e:expr,)*) => ({ /* compiler built-in */ });
722 /// Expands to the line number on which it was invoked.
724 /// For more information, see the documentation for [`std::line!`].
726 /// [`std::line!`]: ../std/macro.line.html
727 #[stable(feature = "rust1", since = "1.0.0")]
728 #[rustc_doc_only_macro]
729 macro_rules! line { () => ({ /* compiler built-in */ }) }
731 /// Expands to the column number on which it was invoked.
733 /// For more information, see the documentation for [`std::column!`].
735 /// [`std::column!`]: ../std/macro.column.html
736 #[stable(feature = "rust1", since = "1.0.0")]
737 #[rustc_doc_only_macro]
738 macro_rules! column { () => ({ /* compiler built-in */ }) }
740 /// Expands to the file name from which it was invoked.
742 /// For more information, see the documentation for [`std::file!`].
744 /// [`std::file!`]: ../std/macro.file.html
745 #[stable(feature = "rust1", since = "1.0.0")]
746 #[rustc_doc_only_macro]
747 macro_rules! file { () => ({ /* compiler built-in */ }) }
749 /// Stringifies its arguments.
751 /// For more information, see the documentation for [`std::stringify!`].
753 /// [`std::stringify!`]: ../std/macro.stringify.html
754 #[stable(feature = "rust1", since = "1.0.0")]
755 #[rustc_doc_only_macro]
756 macro_rules! stringify { ($($t:tt)*) => ({ /* compiler built-in */ }) }
758 /// Includes a utf8-encoded file as a string.
760 /// For more information, see the documentation for [`std::include_str!`].
762 /// [`std::include_str!`]: ../std/macro.include_str.html
763 #[stable(feature = "rust1", since = "1.0.0")]
764 #[rustc_doc_only_macro]
765 macro_rules! include_str {
766 ($file:expr) => ({ /* compiler built-in */ });
767 ($file:expr,) => ({ /* compiler built-in */ });
770 /// Includes a file as a reference to a byte array.
772 /// For more information, see the documentation for [`std::include_bytes!`].
774 /// [`std::include_bytes!`]: ../std/macro.include_bytes.html
775 #[stable(feature = "rust1", since = "1.0.0")]
776 #[rustc_doc_only_macro]
777 macro_rules! include_bytes {
778 ($file:expr) => ({ /* compiler built-in */ });
779 ($file:expr,) => ({ /* compiler built-in */ });
782 /// Expands to a string that represents the current module path.
784 /// For more information, see the documentation for [`std::module_path!`].
786 /// [`std::module_path!`]: ../std/macro.module_path.html
787 #[stable(feature = "rust1", since = "1.0.0")]
788 #[rustc_doc_only_macro]
789 macro_rules! module_path { () => ({ /* compiler built-in */ }) }
791 /// Evaluates boolean combinations of configuration flags, at compile-time.
793 /// For more information, see the documentation for [`std::cfg!`].
795 /// [`std::cfg!`]: ../std/macro.cfg.html
796 #[stable(feature = "rust1", since = "1.0.0")]
797 #[rustc_doc_only_macro]
798 macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
800 /// Parses a file as an expression or an item according to the context.
802 /// For more information, see the documentation for [`std::include!`].
804 /// [`std::include!`]: ../std/macro.include.html
805 #[stable(feature = "rust1", since = "1.0.0")]
806 #[rustc_doc_only_macro]
807 macro_rules! include {
808 ($file:expr) => ({ /* compiler built-in */ });
809 ($file:expr,) => ({ /* compiler built-in */ });
812 /// Asserts that a boolean expression is `true` at runtime.
814 /// For more information, see the documentation for [`std::assert!`].
816 /// [`std::assert!`]: ../std/macro.assert.html
817 #[rustc_doc_only_macro]
818 #[stable(feature = "rust1", since = "1.0.0")]
819 macro_rules! assert {
820 ($cond:expr) => ({ /* compiler built-in */ });
821 ($cond:expr,) => ({ /* compiler built-in */ });
822 ($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ });