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tutorial: Merge discussion of patterns and let bindings

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Brian Anderson 2012-09-24 19:51:03 -07:00
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commit ba8750a550
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@ -580,8 +580,8 @@ you use the matching to get at the contents of data types. Remember
that `(float, float)` is a tuple of two floats:
~~~~
use float::consts::pi;
fn angle(vector: (float, float)) -> float {
let pi = float::consts::pi;
match vector {
(0f, y) if y < 0f => 1.5 * pi,
(0f, y) => 0.5 * pi,
@ -601,23 +601,19 @@ an expression of type `bool` that determines, after the pattern is
found to match, whether the arm is taken or not. The variables bound
by the pattern are available in this guard expression.
## Let
You've already seen simple `let` bindings. `let` is also a little fancier: it
is possible to use destructuring patterns in it. For example, you can say this
to extract the fields from a tuple:
You've already seen simple `let` bindings, but `let` is a little
fancier than you've been led to believe. It too supports destructuring
patterns. For example, you can say this to extract the fields from a
tuple, introducing two variables, `a` and `b`.
~~~~
# fn get_tuple_of_two_ints() -> (int, int) { (1, 1) }
let (a, b) = get_tuple_of_two_ints();
~~~~
This will introduce two new variables, `a` and `b`, bound to the
content of the tuple.
You may only use *irrefutable* patterns—patterns that can never fail to
match—in let bindings. Other types of patterns, such as literals, are
not allowed.
Let bindings only work with _irrefutable_ patterns, that is, patterns
that can never fail to match. This excludes `let` from matching
literals and most enum variants.
## Loops