Rust by Example

Indirectly accessing a variable makes it impossible to branch and use that variable without re-binding. match provides the @ sigil for binding values to names:

// A function `age` which returns a `u32`.

fn age() -> u32 {

15

}

fn main() {

println!("Tell me what type of person you are");

match age() {

0             => println!("I haven't celebrated my first birthday yet"),

// Could `match` 1 ..= 12 directly but then what age

// would the child be? Instead, bind to `n` for the

// sequence of 1 ..= 12. Now the age can be reported.

n @ 1  ..= 12 => println!("I'm a child of age {:?}", n),

n @ 13 ..= 19 => println!("I'm a teen of age {:?}", n),

// Nothing bound. Return the result.

n             => println!("I'm an old person of age {:?}", n),

}

}

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You can also use binding to "destructure" enum variants, such as Option:

fn some_number() -> Option {

Some(42)

}

fn main() {

match some_number() {

// Got `Some` variant, match if its value, bound to `n`,

// is equal to 42.

Some(n @ 42) => println!("The Answer: {}!", n),

// Match any other number.

Some(n)      => println!("Not interesting... {}", n),

// Match anything else (`None` variant).

_            => (),

}

}

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