src/libcore/macros.rs

   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.
   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 /// Entry point of thread panic, for details, see std::macros
  12 #[macro_export]
  13 #[allow_internal_unstable]
  14 macro_rules! panic {
  15     () => (
  16         panic!("explicit panic")
  17     );
  18     ($msg:expr) => ({
  19         static _MSG_FILE_LINE: (&'static str, &'static str, u32) = ($msg, file!(), line!());
  20         $crate::panicking::panic(&_MSG_FILE_LINE)
  21     });
  22     ($fmt:expr, $($arg:tt)*) => ({
  23         // The leading _'s are to avoid dead code warnings if this is
  24         // used inside a dead function. Just `#[allow(dead_code)]` is
  25         // insufficient, since the user may have
  26         // `#[forbid(dead_code)]` and which cannot be overridden.
  27         static _FILE_LINE: (&'static str, u32) = (file!(), line!());
  28         $crate::panicking::panic_fmt(format_args!($fmt, $($arg)*), &_FILE_LINE)
  29     });
  30 }
  31
  32 /// Ensure that a boolean expression is `true` at runtime.
  33 ///
  34 /// This will invoke the `panic!` macro if the provided expression cannot be
  35 /// evaluated to `true` at runtime.
  36 ///
  37 /// # Examples
  38 ///
  39 /// ```
  40 /// // the panic message for these assertions is the stringified value of the
  41 /// // expression given.
  42 /// assert!(true);
  43 ///
  44 /// fn some_computation() -> bool { true } // a very simple function
  45 ///
  46 /// assert!(some_computation());
  47 ///
  48 /// // assert with a custom message
  49 /// let x = true;
  50 /// assert!(x, "x wasn't true!");
  51 ///
  52 /// let a = 3; let b = 27;
  53 /// assert!(a + b == 30, "a = {}, b = {}", a, b);
  54 /// ```
  55 #[macro_export]
  56 #[stable(feature = "rust1", since = "1.0.0")]
  57 macro_rules! assert {
  58     ($cond:expr) => (
  59         if !$cond {
  60             panic!(concat!("assertion failed: ", stringify!($cond)))
  61         }
  62     );
  63     ($cond:expr, $($arg:tt)+) => (
  64         if !$cond {
  65             panic!($($arg)+)
  66         }
  67     );
  68 }
  69
  70 /// Asserts that two expressions are equal to each other.
  71 ///
  72 /// On panic, this macro will print the values of the expressions with their
  73 /// debug representations.
  74 ///
  75 /// # Examples
  76 ///
  77 /// ```
  78 /// let a = 3;
  79 /// let b = 1 + 2;
  80 /// assert_eq!(a, b);
  81 /// ```
  82 #[macro_export]
  83 #[stable(feature = "rust1", since = "1.0.0")]
  84 macro_rules! assert_eq {
  85     ($left:expr , $right:expr) => ({
  86         match (&($left), &($right)) {
  87             (left_val, right_val) => {
  88                 if !(*left_val == *right_val) {
  89                     panic!("assertion failed: `(left == right)` \
  90                            (left: `{:?}`, right: `{:?}`)", *left_val, *right_val)
  91                 }
  92             }
  93         }
  94     })
  95 }
  96
  97 /// Ensure that a boolean expression is `true` at runtime.
  98 ///
  99 /// This will invoke the `panic!` macro if the provided expression cannot be
 100 /// evaluated to `true` at runtime.
 101 ///
 102 /// Unlike `assert!`, `debug_assert!` statements are only enabled in non
 103 /// optimized builds by default. An optimized build will omit all
 104 /// `debug_assert!` statements unless `-C debug-assertions` is passed to the
 105 /// compiler. This makes `debug_assert!` useful for checks that are too
 106 /// expensive to be present in a release build but may be helpful during
 107 /// development.
 108 ///
 109 /// # Examples
 110 ///
 111 /// ```
 112 /// // the panic message for these assertions is the stringified value of the
 113 /// // expression given.
 114 /// debug_assert!(true);
 115 ///
 116 /// fn some_expensive_computation() -> bool { true } // a very simple function
 117 /// debug_assert!(some_expensive_computation());
 118 ///
 119 /// // assert with a custom message
 120 /// let x = true;
 121 /// debug_assert!(x, "x wasn't true!");
 122 ///
 123 /// let a = 3; let b = 27;
 124 /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
 125 /// ```
 126 #[macro_export]
 127 #[stable(feature = "rust1", since = "1.0.0")]
 128 macro_rules! debug_assert {
 129     ($($arg:tt)*) => (if cfg!(debug_assertions) { assert!($($arg)*); })
 130 }
 131
 132 /// Asserts that two expressions are equal to each other, testing equality in
 133 /// both directions.
 134 ///
 135 /// On panic, this macro will print the values of the expressions.
 136 ///
 137 /// Unlike `assert_eq!`, `debug_assert_eq!` statements are only enabled in non
 138 /// optimized builds by default. An optimized build will omit all
 139 /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
 140 /// compiler. This makes `debug_assert_eq!` useful for checks that are too
 141 /// expensive to be present in a release build but may be helpful during
 142 /// development.
 143 ///
 144 /// # Examples
 145 ///
 146 /// ```
 147 /// let a = 3;
 148 /// let b = 1 + 2;
 149 /// debug_assert_eq!(a, b);
 150 /// ```
 151 #[macro_export]
 152 macro_rules! debug_assert_eq {
 153     ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_eq!($($arg)*); })
 154 }
 155
 156 /// Short circuiting evaluation on Err
 157 ///
 158 /// `libstd` contains a more general `try!` macro that uses `From<E>`.
 159 #[macro_export]
 160 macro_rules! try {
 161     ($e:expr) => ({
 162         use $crate::result::Result::{Ok, Err};
 163
 164         match $e {
 165             Ok(e) => e,
 166             Err(e) => return Err(e),
 167         }
 168     })
 169 }
 170
 171 /// Use the `format!` syntax to write data into a buffer of type `&mut Write`.
 172 /// See `std::fmt` for more information.
 173 ///
 174 /// # Examples
 175 ///
 176 /// ```
 177 /// use std::io::Write;
 178 ///
 179 /// let mut w = Vec::new();
 180 /// write!(&mut w, "test").unwrap();
 181 /// write!(&mut w, "formatted {}", "arguments").unwrap();
 182 /// ```
 183 #[macro_export]
 184 macro_rules! write {
 185     ($dst:expr, $($arg:tt)*) => ($dst.write_fmt(format_args!($($arg)*)))
 186 }
 187
 188 /// Equivalent to the `write!` macro, except that a newline is appended after
 189 /// the message is written.
 190 #[macro_export]
 191 #[stable(feature = "rust1", since = "1.0.0")]
 192 macro_rules! writeln {
 193     ($dst:expr, $fmt:expr) => (
 194         write!($dst, concat!($fmt, "\n"))
 195     );
 196     ($dst:expr, $fmt:expr, $($arg:tt)*) => (
 197         write!($dst, concat!($fmt, "\n"), $($arg)*)
 198     );
 199 }
 200
 201 /// A utility macro for indicating unreachable code.
 202 ///
 203 /// This is useful any time that the compiler can't determine that some code is unreachable. For
 204 /// example:
 205 ///
 206 /// * Match arms with guard conditions.
 207 /// * Loops that dynamically terminate.
 208 /// * Iterators that dynamically terminate.
 209 ///
 210 /// # Panics
 211 ///
 212 /// This will always panic.
 213 ///
 214 /// # Examples
 215 ///
 216 /// Match arms:
 217 ///
 218 /// ```
 219 /// fn foo(x: Option<i32>) {
 220 ///     match x {
 221 ///         Some(n) if n >= 0 => println!("Some(Non-negative)"),
 222 ///         Some(n) if n <  0 => println!("Some(Negative)"),
 223 ///         Some(_)           => unreachable!(), // compile error if commented out
 224 ///         None              => println!("None")
 225 ///     }
 226 /// }
 227 /// ```
 228 ///
 229 /// Iterators:
 230 ///
 231 /// ```
 232 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
 233 ///     for i in 0.. {
 234 ///         if 3*i < i { panic!("u32 overflow"); }
 235 ///         if x < 3*i { return i-1; }
 236 ///     }
 237 ///     unreachable!();
 238 /// }
 239 /// ```
 240 #[macro_export]
 241 #[unstable(feature = "core",
 242            reason = "relationship with panic is unclear")]
 243 macro_rules! unreachable {
 244     () => ({
 245         panic!("internal error: entered unreachable code")
 246     });
 247     ($msg:expr) => ({
 248         unreachable!("{}", $msg)
 249     });
 250     ($fmt:expr, $($arg:tt)*) => ({
 251         panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
 252     });
 253 }
 254
 255 /// A standardised placeholder for marking unfinished code. It panics with the
 256 /// message `"not yet implemented"` when executed.
 257 #[macro_export]
 258 #[unstable(feature = "core",
 259            reason = "relationship with panic is unclear")]
 260 macro_rules! unimplemented {
 261     () => (panic!("not yet implemented"))
 262 }