rust/src/doc/trpl/patterns.md

% Patterns

Patterns are quite common in Rust. We use them in [variable
bindings][bindings], [match statements][match], and other places, too. Let’s go
on a whirlwind tour of all of the things patterns can do!

[bindings]: variable-bindings.html
[match]: match.html

A quick refresher: you can match against literals directly, and `_` acts as an
‘any’ case:

```rust
let x = 1;

match x {
    1 => println!("one"),
    2 => println!("two"),
    3 => println!("three"),
    _ => println!("anything"),
}
```

# Multiple patterns

You can match multiple patterns with `|`:

```rust
let x = 1;

match x {
    1 | 2 => println!("one or two"),
    3 => println!("three"),
    _ => println!("anything"),
}
```

# Ranges

You can match a range of values with `...`:

```rust
let x = 1;

match x {
    1 ... 5 => println!("one through five"),
    _ => println!("anything"),
}
```

Ranges are mostly used with integers and single characters.

# Bindings

If you’re matching multiple things, via a `|` or a `...`, you can bind
the value to a name with `@`:

```rust
let x = 1;

match x {
    e @ 1 ... 5 => println!("got a range element {}", e),
    _ => println!("anything"),
}
```

# Ignoring variants

If you’re matching on an enum which has variants, you can use `..` to
ignore the value and type in the variant:

```rust
enum OptionalInt {
    Value(i32),
    Missing,
}

let x = OptionalInt::Value(5);

match x {
    OptionalInt::Value(..) => println!("Got an int!"),
    OptionalInt::Missing => println!("No such luck."),
}
```

# Guards

You can introduce ‘match guards’ with `if`:

```rust
enum OptionalInt {
    Value(i32),
    Missing,
}

let x = OptionalInt::Value(5);

match x {
    OptionalInt::Value(i) if i > 5 => println!("Got an int bigger than five!"),
    OptionalInt::Value(..) => println!("Got an int!"),
    OptionalInt::Missing => println!("No such luck."),
}
```

# ref and ref mut

If you want to get a [reference][ref], use the `ref` keyword:

```rust
let x = 5;

match x {
    ref r => println!("Got a reference to {}", r),
}
```

[ref]: references-and-borrowing.html

Here, the `r` inside the `match` has the type `&i32`. In other words, the `ref`
keyword _creates_ a reference, for use in the pattern. If you need a mutable
reference, `ref mut` will work in the same way:

```rust
let mut x = 5;

match x {
    ref mut mr => println!("Got a mutable reference to {}", mr),
}
```

# Destructuring

If you have a compound data type, like a `struct`, you can destructure it
inside of a pattern:

```rust
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

match origin {
    Point { x: x, y: y } => println!("({},{})", x, y),
}
```

If we only care about some of the values, we don’t have to give them all names:

```rust
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

match origin {
    Point { x: x, .. } => println!("x is {}", x),
}
```

You can do this kind of match on any member, not just the first:

```rust
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

match origin {
    Point { y: y, .. } => println!("y is {}", y),
}
```

This ‘destructuring’ behavior works on any compound data type, like
[tuples][tuples] or [enums][enums].

[tuples]: primitive-types.html#tuples
[enums]: enums.html

# Mix and Match

Whew! That’s a lot of different ways to match things, and they can all be
mixed and matched, depending on what you’re doing:

```{rust,ignore}
match x {
    Foo { x: Some(ref name), y: None } => ...
}
```

Patterns are very powerful.  Make good use of them.