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Diffstat (limited to 'library/std/src/macros.rs')
| -rw-r--r-- | library/std/src/macros.rs | 313 |
1 files changed, 313 insertions, 0 deletions
diff --git a/library/std/src/macros.rs b/library/std/src/macros.rs new file mode 100644 index 00000000000..724dbada930 --- /dev/null +++ b/library/std/src/macros.rs @@ -0,0 +1,313 @@ +//! Standard library macros +//! +//! This modules contains a set of macros which are exported from the standard +//! library. Each macro is available for use when linking against the standard +//! library. + +#[doc(include = "../../core/src/macros/panic.md")] +#[macro_export] +#[stable(feature = "rust1", since = "1.0.0")] +#[allow_internal_unstable(libstd_sys_internals)] +macro_rules! panic { + () => ({ $crate::panic!("explicit panic") }); + ($msg:expr) => ({ $crate::rt::begin_panic($msg) }); + ($msg:expr,) => ({ $crate::panic!($msg) }); + ($fmt:expr, $($arg:tt)+) => ({ + $crate::rt::begin_panic_fmt(&$crate::format_args!($fmt, $($arg)+)) + }); +} + +/// Prints to the standard output. +/// +/// Equivalent to the [`println!`] macro except that a newline is not printed at +/// the end of the message. +/// +/// Note that stdout is frequently line-buffered by default so it may be +/// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted +/// immediately. +/// +/// Use `print!` only for the primary output of your program. Use +/// [`eprint!`] instead to print error and progress messages. +/// +/// [`println!`]: ../std/macro.println.html +/// [flush]: ../std/io/trait.Write.html#tymethod.flush +/// [`eprint!`]: ../std/macro.eprint.html +/// +/// # Panics +/// +/// Panics if writing to `io::stdout()` fails. +/// +/// # Examples +/// +/// ``` +/// use std::io::{self, Write}; +/// +/// print!("this "); +/// print!("will "); +/// print!("be "); +/// print!("on "); +/// print!("the "); +/// print!("same "); +/// print!("line "); +/// +/// io::stdout().flush().unwrap(); +/// +/// print!("this string has a newline, why not choose println! instead?\n"); +/// +/// io::stdout().flush().unwrap(); +/// ``` +#[macro_export] +#[stable(feature = "rust1", since = "1.0.0")] +#[allow_internal_unstable(print_internals)] +macro_rules! print { + ($($arg:tt)*) => ($crate::io::_print($crate::format_args!($($arg)*))); +} + +/// Prints to the standard output, with a newline. +/// +/// On all platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone +/// (no additional CARRIAGE RETURN (`\r`/`U+000D`)). +/// +/// Use the [`format!`] syntax to write data to the standard output. +/// See [`std::fmt`] for more information. +/// +/// Use `println!` only for the primary output of your program. Use +/// [`eprintln!`] instead to print error and progress messages. +/// +/// [`format!`]: ../std/macro.format.html +/// [`std::fmt`]: ../std/fmt/index.html +/// [`eprintln!`]: ../std/macro.eprintln.html +/// # Panics +/// +/// Panics if writing to `io::stdout` fails. +/// +/// # Examples +/// +/// ``` +/// println!(); // prints just a newline +/// println!("hello there!"); +/// println!("format {} arguments", "some"); +/// ``` +#[macro_export] +#[stable(feature = "rust1", since = "1.0.0")] +#[allow_internal_unstable(print_internals, format_args_nl)] +macro_rules! println { + () => ($crate::print!("\n")); + ($($arg:tt)*) => ({ + $crate::io::_print($crate::format_args_nl!($($arg)*)); + }) +} + +/// Prints to the standard error. +/// +/// Equivalent to the [`print!`] macro, except that output goes to +/// [`io::stderr`] instead of `io::stdout`. See [`print!`] for +/// example usage. +/// +/// Use `eprint!` only for error and progress messages. Use `print!` +/// instead for the primary output of your program. +/// +/// [`io::stderr`]: ../std/io/struct.Stderr.html +/// [`print!`]: ../std/macro.print.html +/// +/// # Panics +/// +/// Panics if writing to `io::stderr` fails. +/// +/// # Examples +/// +/// ``` +/// eprint!("Error: Could not complete task"); +/// ``` +#[macro_export] +#[stable(feature = "eprint", since = "1.19.0")] +#[allow_internal_unstable(print_internals)] +macro_rules! eprint { + ($($arg:tt)*) => ($crate::io::_eprint($crate::format_args!($($arg)*))); +} + +/// Prints to the standard error, with a newline. +/// +/// Equivalent to the [`println!`] macro, except that output goes to +/// [`io::stderr`] instead of `io::stdout`. See [`println!`] for +/// example usage. +/// +/// Use `eprintln!` only for error and progress messages. Use `println!` +/// instead for the primary output of your program. +/// +/// [`io::stderr`]: ../std/io/struct.Stderr.html +/// [`println!`]: ../std/macro.println.html +/// +/// # Panics +/// +/// Panics if writing to `io::stderr` fails. +/// +/// # Examples +/// +/// ``` +/// eprintln!("Error: Could not complete task"); +/// ``` +#[macro_export] +#[stable(feature = "eprint", since = "1.19.0")] +#[allow_internal_unstable(print_internals, format_args_nl)] +macro_rules! eprintln { + () => ($crate::eprint!("\n")); + ($($arg:tt)*) => ({ + $crate::io::_eprint($crate::format_args_nl!($($arg)*)); + }) +} + +/// Prints and returns the value of a given expression for quick and dirty +/// debugging. +/// +/// An example: +/// +/// ```rust +/// let a = 2; +/// let b = dbg!(a * 2) + 1; +/// // ^-- prints: [src/main.rs:2] a * 2 = 4 +/// assert_eq!(b, 5); +/// ``` +/// +/// The macro works by using the `Debug` implementation of the type of +/// the given expression to print the value to [stderr] along with the +/// source location of the macro invocation as well as the source code +/// of the expression. +/// +/// Invoking the macro on an expression moves and takes ownership of it +/// before returning the evaluated expression unchanged. If the type +/// of the expression does not implement `Copy` and you don't want +/// to give up ownership, you can instead borrow with `dbg!(&expr)` +/// for some expression `expr`. +/// +/// The `dbg!` macro works exactly the same in release builds. +/// This is useful when debugging issues that only occur in release +/// builds or when debugging in release mode is significantly faster. +/// +/// Note that the macro is intended as a debugging tool and therefore you +/// should avoid having uses of it in version control for long periods. +/// Use cases involving debug output that should be added to version control +/// are better served by macros such as [`debug!`] from the [`log`] crate. +/// +/// # Stability +/// +/// The exact output printed by this macro should not be relied upon +/// and is subject to future changes. +/// +/// # Panics +/// +/// Panics if writing to `io::stderr` fails. +/// +/// # Further examples +/// +/// With a method call: +/// +/// ```rust +/// fn foo(n: usize) { +/// if let Some(_) = dbg!(n.checked_sub(4)) { +/// // ... +/// } +/// } +/// +/// foo(3) +/// ``` +/// +/// This prints to [stderr]: +/// +/// ```text,ignore +/// [src/main.rs:4] n.checked_sub(4) = None +/// ``` +/// +/// Naive factorial implementation: +/// +/// ```rust +/// fn factorial(n: u32) -> u32 { +/// if dbg!(n <= 1) { +/// dbg!(1) +/// } else { +/// dbg!(n * factorial(n - 1)) +/// } +/// } +/// +/// dbg!(factorial(4)); +/// ``` +/// +/// This prints to [stderr]: +/// +/// ```text,ignore +/// [src/main.rs:3] n <= 1 = false +/// [src/main.rs:3] n <= 1 = false +/// [src/main.rs:3] n <= 1 = false +/// [src/main.rs:3] n <= 1 = true +/// [src/main.rs:4] 1 = 1 +/// [src/main.rs:5] n * factorial(n - 1) = 2 +/// [src/main.rs:5] n * factorial(n - 1) = 6 +/// [src/main.rs:5] n * factorial(n - 1) = 24 +/// [src/main.rs:11] factorial(4) = 24 +/// ``` +/// +/// The `dbg!(..)` macro moves the input: +/// +/// ```compile_fail +/// /// A wrapper around `usize` which importantly is not Copyable. +/// #[derive(Debug)] +/// struct NoCopy(usize); +/// +/// let a = NoCopy(42); +/// let _ = dbg!(a); // <-- `a` is moved here. +/// let _ = dbg!(a); // <-- `a` is moved again; error! +/// ``` +/// +/// You can also use `dbg!()` without a value to just print the +/// file and line whenever it's reached. +/// +/// Finally, if you want to `dbg!(..)` multiple values, it will treat them as +/// a tuple (and return it, too): +/// +/// ``` +/// assert_eq!(dbg!(1usize, 2u32), (1, 2)); +/// ``` +/// +/// However, a single argument with a trailing comma will still not be treated +/// as a tuple, following the convention of ignoring trailing commas in macro +/// invocations. You can use a 1-tuple directly if you need one: +/// +/// ``` +/// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored +/// assert_eq!((1,), dbg!((1u32,))); // 1-tuple +/// ``` +/// +/// [stderr]: https://en.wikipedia.org/wiki/Standard_streams#Standard_error_(stderr) +/// [`debug!`]: https://docs.rs/log/*/log/macro.debug.html +/// [`log`]: https://crates.io/crates/log +#[macro_export] +#[stable(feature = "dbg_macro", since = "1.32.0")] +macro_rules! dbg { + () => { + $crate::eprintln!("[{}:{}]", $crate::file!(), $crate::line!()); + }; + ($val:expr) => { + // Use of `match` here is intentional because it affects the lifetimes + // of temporaries - https://stackoverflow.com/a/48732525/1063961 + match $val { + tmp => { + $crate::eprintln!("[{}:{}] {} = {:#?}", + $crate::file!(), $crate::line!(), $crate::stringify!($val), &tmp); + tmp + } + } + }; + // Trailing comma with single argument is ignored + ($val:expr,) => { $crate::dbg!($val) }; + ($($val:expr),+ $(,)?) => { + ($($crate::dbg!($val)),+,) + }; +} + +#[cfg(test)] +macro_rules! assert_approx_eq { + ($a:expr, $b:expr) => {{ + let (a, b) = (&$a, &$b); + assert!((*a - *b).abs() < 1.0e-6, "{} is not approximately equal to {}", *a, *b); + }}; +} |