Rust for C-Programmers

21.14 if let and while let

When you only care about matching one pattern and ignoring everything else, if let and while let offer convenient shortcuts over a full match.

21.14.1 if let Without else

fn main() {
    let some_option = Some(5);

    // Using match
    match some_option {
        Some(value) => println!("The value is {}", value),
        _ => (),
    }

    // Equivalent if let
    if let Some(value) = some_option {
        println!("The value is {}", value);
    }
}

21.14.2 if let With else

fn main() {
    let some_option = Some(5);
    if let Some(value) = some_option {
        println!("The value is {}", value);
    } else {
        println!("No value!");
    }
}

Combining if let, else if, and else if let

fn main() {
    let some_option = Some(5);
    let another_value = 10;

    if let Some(value) = some_option {
        println!("Matched Some({})", value);
    } else if another_value == 10 {
        println!("another_value is 10");
    } else if let None = some_option {
        println!("Matched None");
    } else {
        println!("No match");
    }
}

21.14.3 while let

while let repeatedly matches the same pattern as long as it succeeds:

fn main() {
    let mut numbers = vec![1, 2, 3];
    while let Some(num) = numbers.pop() {
        println!("Got {}", num);
    }
    println!("No more numbers!");
}