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Rollup merge of #24750 - withoutboats:patch-1, r=steveklabnik

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1) Moved 'while' section below 'loop', 'break', and 'continue'; 2) Added information to 'while' and 'for' loops that they interact with 'break' and 'continue' and may have a lifetime label. 3) Clarified labeling syntax on the infinite loops.
This commit is contained in:
Manish Goregaokar 2015-04-24 09:49:27 +05:30
commit 76dd69183f
1 changed files with 53 additions and 42 deletions
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src/doc/reference.md
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@ -3081,6 +3081,50 @@ fn ten_times<F>(f: F) where F: Fn(i32) {
ten_times(|j| println!("hello, {}", j));
```
### Infinite loops
A `loop` expression denotes an infinite loop.
```{.ebnf .gram}
loop_expr : [ lifetime ':' ] "loop" '{' block '}';
```
A `loop` expression may optionally have a _label_. The label is written as
a lifetime preceding the loop expression, as in `'foo: loop{ }`. If a
label is present, then labeled `break` and `continue` expressions nested
within this loop may exit out of this loop or return control to its head.
See [Break expressions](#break-expressions) and [Continue
expressions](#continue-expressions).
### Break expressions
```{.ebnf .gram}
break_expr : "break" [ lifetime ];
```
A `break` expression has an optional _label_. If the label is absent, then
executing a `break` expression immediately terminates the innermost loop
enclosing it. It is only permitted in the body of a loop. If the label is
present, then `break 'foo` terminates the loop with label `'foo`, which need not
be the innermost label enclosing the `break` expression, but must enclose it.
### Continue expressions
```{.ebnf .gram}
continue_expr : "continue" [ lifetime ];
```
A `continue` expression has an optional _label_. If the label is absent, then
executing a `continue` expression immediately terminates the current iteration
of the innermost loop enclosing it, returning control to the loop *head*. In
the case of a `while` loop, the head is the conditional expression controlling
the loop. In the case of a `for` loop, the head is the call-expression
controlling the loop. If the label is present, then `continue 'foo` returns
control to the head of the loop with label `'foo`, which need not be the
innermost label enclosing the `break` expression, but must enclose it.
A `continue` expression is only permitted in the body of a loop.
### While loops
```{.ebnf .gram}
@ -3103,48 +3147,10 @@ while i < 10 {
}
```
### Infinite loops
A `loop` expression denotes an infinite loop.
```{.ebnf .gram}
loop_expr : [ lifetime ':' ] "loop" '{' block '}';
```
A `loop` expression may optionally have a _label_. If a label is present, then
labeled `break` and `continue` expressions nested within this loop may exit out
of this loop or return control to its head. See [Break
expressions](#break-expressions) and [Continue
expressions](#continue-expressions).
### Break expressions
```{.ebnf .gram}
break_expr : "break" [ lifetime ];
```
A `break` expression has an optional _label_. If the label is absent, then
executing a `break` expression immediately terminates the innermost loop
enclosing it. It is only permitted in the body of a loop. If the label is
present, then `break foo` terminates the loop with label `foo`, which need not
be the innermost label enclosing the `break` expression, but must enclose it.
### Continue expressions
```{.ebnf .gram}
continue_expr : "continue" [ lifetime ];
```
A `continue` expression has an optional _label_. If the label is absent, then
executing a `continue` expression immediately terminates the current iteration
of the innermost loop enclosing it, returning control to the loop *head*. In
the case of a `while` loop, the head is the conditional expression controlling
the loop. In the case of a `for` loop, the head is the call-expression
controlling the loop. If the label is present, then `continue foo` returns
control to the head of the loop with label `foo`, which need not be the
innermost label enclosing the `break` expression, but must enclose it.
A `continue` expression is only permitted in the body of a loop.
Like `loop` expressions, `while` loops can be controlled with `break` or
`continue`, and may optionally have a _label_. See [infinite
loops](#infinite-loops), [break expressions](#break-expressions), and
[continue expressions](#continue-expressions) for more information.
### For expressions
@ -3180,6 +3186,11 @@ for i in 0..256 {
}
```
Like `loop` expressions, `for` loops can be controlled with `break` or
`continue`, and may optionally have a _label_. See [infinite
loops](#infinite-loops), [break expressions](#break-expressions), and
[continue expressions](#continue-expressions) for more information.
### If expressions
```{.ebnf .gram}