@@ -30,69 +30,224 @@ macro_rules! panic {
3030 } ) ;
3131}
3232
33- /// Runtime assertion, for details see std::macros
33+ /// Ensure that a boolean expression is `true` at runtime.
34+ ///
35+ /// This will invoke the `panic!` macro if the provided expression cannot be
36+ /// evaluated to `true` at runtime.
37+ ///
38+ /// # Example
39+ ///
40+ /// ```
41+ /// // the panic message for these assertions is the stringified value of the
42+ /// // expression given.
43+ /// assert!(true);
44+ /// # fn some_computation() -> bool { true }
45+ /// assert!(some_computation());
46+ ///
47+ /// // assert with a custom message
48+ /// # let x = true;
49+ /// assert!(x, "x wasn't true!");
50+ /// # let a = 3i; let b = 27i;
51+ /// assert!(a + b == 30, "a = {}, b = {}", a, b);
52+ /// ```
3453#[ macro_export]
3554macro_rules! assert {
3655 ( $cond: expr) => (
3756 if !$cond {
3857 panic!( concat!( "assertion failed: " , stringify!( $cond) ) )
3958 }
4059 ) ;
41- ( $cond: expr, $( $arg: tt ) * ) => (
60+ ( $cond: expr, $( $arg: expr ) ,+ ) => (
4261 if !$cond {
43- panic!( $( $arg) * )
62+ panic!( $( $arg) ,+ )
4463 }
4564 ) ;
4665}
4766
48- /// Runtime assertion for equality, for details see std::macros
67+ /// Asserts that two expressions are equal to each other, testing equality in
68+ /// both directions.
69+ ///
70+ /// On panic, this macro will print the values of the expressions.
71+ ///
72+ /// # Example
73+ ///
74+ /// ```
75+ /// let a = 3i;
76+ /// let b = 1i + 2i;
77+ /// assert_eq!(a, b);
78+ /// ```
4979#[ macro_export]
5080macro_rules! assert_eq {
51- ( $cond1: expr, $cond2: expr) => ( {
52- let c1 = $cond1;
53- let c2 = $cond2;
54- if c1 != c2 || c2 != c1 {
55- panic!( "expressions not equal, left: {}, right: {}" , c1, c2) ;
81+ ( $left: expr , $right: expr) => ( {
82+ match ( & ( $left) , & ( $right) ) {
83+ ( left_val, right_val) => {
84+ // check both directions of equality....
85+ if !( ( * left_val == * right_val) &&
86+ ( * right_val == * left_val) ) {
87+ panic!( "assertion failed: `(left == right) && (right == left)` \
88+ , * left_val, * right_val)
89+ }
90+ }
5691 }
5792 } )
5893}
5994
60- /// Runtime assertion for equality, only without `--cfg ndebug`
95+ /// Ensure that a boolean expression is `true` at runtime.
96+ ///
97+ /// This will invoke the `panic!` macro if the provided expression cannot be
98+ /// evaluated to `true` at runtime.
99+ ///
100+ /// Unlike `assert!`, `debug_assert!` statements can be disabled by passing
101+ /// `--cfg ndebug` to the compiler. This makes `debug_assert!` useful for
102+ /// checks that are too expensive to be present in a release build but may be
103+ /// helpful during development.
104+ ///
105+ /// # Example
106+ ///
107+ /// ```
108+ /// // the panic message for these assertions is the stringified value of the
109+ /// // expression given.
110+ /// debug_assert!(true);
111+ /// # fn some_expensive_computation() -> bool { true }
112+ /// debug_assert!(some_expensive_computation());
113+ ///
114+ /// // assert with a custom message
115+ /// # let x = true;
116+ /// debug_assert!(x, "x wasn't true!");
117+ /// # let a = 3i; let b = 27i;
118+ /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
119+ /// ```
120+ #[ macro_export]
121+ macro_rules! debug_assert {
122+ ( $( $arg: tt) * ) => ( if cfg!( not( ndebug) ) { assert!( $( $arg) * ) ; } )
123+ }
124+
125+ /// Asserts that two expressions are equal to each other, testing equality in
126+ /// both directions.
127+ ///
128+ /// On panic, this macro will print the values of the expressions.
129+ ///
130+ /// Unlike `assert_eq!`, `debug_assert_eq!` statements can be disabled by
131+ /// passing `--cfg ndebug` to the compiler. This makes `debug_assert_eq!`
132+ /// useful for checks that are too expensive to be present in a release build
133+ /// but may be helpful during development.
134+ ///
135+ /// # Example
136+ ///
137+ /// ```
138+ /// let a = 3i;
139+ /// let b = 1i + 2i;
140+ /// debug_assert_eq!(a, b);
141+ /// ```
61142#[ macro_export]
62143macro_rules! debug_assert_eq {
63- ( $( $a: tt) * ) => ( {
64- if cfg!( not( ndebug) ) {
65- assert_eq!( $( $a) * ) ;
66- }
67- } )
144+ ( $( $arg: tt) * ) => ( if cfg!( not( ndebug) ) { assert_eq!( $( $arg) * ) ; } )
68145}
69146
70- /// Runtime assertion, disableable at compile time with `-- cfg ndebug`
147+ # [ cfg( stage0 ) ]
71148#[ macro_export]
72- macro_rules! debug_assert {
73- ( $( $arg : tt ) * ) => ( if cfg! ( not ( ndebug ) ) { assert! ( $ ( $arg ) * ) ; } )
149+ macro_rules! try {
150+ ( $e : expr ) => ( match $e { Ok ( e ) => e , Err ( e ) => return Err ( e ) } )
74151}
75152
76153/// Short circuiting evaluation on Err
154+ ///
155+ /// `libstd` contains a more general `try!` macro that uses `FromError`.
156+ #[ cfg( not( stage0) ) ]
77157#[ macro_export]
78158macro_rules! try {
79- ( $e: expr) => ( match $e { Ok ( e) => e, Err ( e) => return Err ( e) } )
159+ ( $e: expr) => ( {
160+ use $crate:: result:: Result :: { Ok , Err } ;
161+
162+ match $e {
163+ Ok ( e) => e,
164+ Err ( e) => return Err ( e) ,
165+ }
166+ } )
80167}
81168
82- /// Writing a formatted string into a writer
169+ /// Use the `format!` syntax to write data into a buffer of type `&mut Writer`.
170+ /// See `std::fmt` for more information.
171+ ///
172+ /// # Example
173+ ///
174+ /// ```
175+ /// # #![allow(unused_must_use)]
176+ ///
177+ /// let mut w = Vec::new();
178+ /// write!(&mut w, "test");
179+ /// write!(&mut w, "formatted {}", "arguments");
180+ /// ```
83181#[ macro_export]
84182macro_rules! write {
85183 ( $dst: expr, $( $arg: tt) * ) => ( ( & mut * $dst) . write_fmt( format_args!( $( $arg) * ) ) )
86184}
87185
88- /// Writing a formatted string plus a newline into a writer
186+ /// Equivalent to the `write!` macro, except that a newline is appended after
187+ /// the message is written.
89188#[ macro_export]
189+ #[ stable]
90190macro_rules! writeln {
91191 ( $dst: expr, $fmt: expr $( $arg: tt) * ) => (
92192 write!( $dst, concat!( $fmt, "\n " ) $( $arg) * )
93193 )
94194}
95195
196+ /// A utility macro for indicating unreachable code.
197+ ///
198+ /// This is useful any time that the compiler can't determine that some code is unreachable. For
199+ /// example:
200+ ///
201+ /// * Match arms with guard conditions.
202+ /// * Loops that dynamically terminate.
203+ /// * Iterators that dynamically terminate.
204+ ///
205+ /// # Panics
206+ ///
207+ /// This will always panic.
208+ ///
209+ /// # Examples
210+ ///
211+ /// Match arms:
212+ ///
213+ /// ```rust
214+ /// fn foo(x: Option<int>) {
215+ /// match x {
216+ /// Some(n) if n >= 0 => println!("Some(Non-negative)"),
217+ /// Some(n) if n < 0 => println!("Some(Negative)"),
218+ /// Some(_) => unreachable!(), // compile error if commented out
219+ /// None => println!("None")
220+ /// }
221+ /// }
222+ /// ```
223+ ///
224+ /// Iterators:
225+ ///
226+ /// ```rust
227+ /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
228+ /// for i in std::iter::count(0_u32, 1) {
229+ /// if 3*i < i { panic!("u32 overflow"); }
230+ /// if x < 3*i { return i-1; }
231+ /// }
232+ /// unreachable!();
233+ /// }
234+ /// ```
96235#[ macro_export]
97- macro_rules! unreachable { ( ) => ( panic!( "unreachable code" ) ) }
236+ macro_rules! unreachable {
237+ ( ) => ( {
238+ panic!( "internal error: entered unreachable code" )
239+ } ) ;
240+ ( $msg: expr) => ( {
241+ unreachable!( "{}" , $msg)
242+ } ) ;
243+ ( $fmt: expr, $( $arg: tt) * ) => ( {
244+ panic!( concat!( "internal error: entered unreachable code: " , $fmt) , $( $arg) * )
245+ } ) ;
246+ }
98247
248+ /// A standardised placeholder for marking unfinished code. It panics with the
249+ /// message `"not yet implemented"` when executed.
250+ #[ macro_export]
251+ macro_rules! unimplemented {
252+ ( ) => ( panic!( "not yet implemented" ) )
253+ }
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