Rust - Expressions - If Let

The if let is the little sibling to match. if let allows you to match only one arm of a match expression. The if let expression takes a pattern on the left hand side of an EQUAL SIGN and an expression on the right hand side of an EQUAL SIGN.

if let can also be combined with normal if-else statements.

Example:

#[derive(Debug)]
enum Breed {
    Husky,
    Poodle,
    Lab,
    // Etc.
}

enum Animal {
    Cat,
    Giraffe,
    Dog(Breed), // This Animal::Dog type contains Breed data
}

fn main() {
    // Example A
    let some_i32 = Some(17i32); // Make 17 an i32 type
    if let Some(3) = some_i32 { // Notice the "=" sign
        println!("Three!");
    } else {
        println!("The number was not three :(");
    }

    // Example B
    let dog = Animal::Dog(Breed::Husky);
    if let Animal::Dog(breed) = dog {
        println!("We found a {:?} dog!", breed);
    }
}