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Difference between if and if-let in Rust

An if let expression is semantically similar to an if expression but in place of a condition expression it expects the keyword let followed by a pattern, an = and a scrutinee expression. If the value of the scrutinee matches the pattern, the corresponding block will execute. Otherwise, flow proceeds to the following else block if it exists. Like if expressions, if let expressions have a value determined by the block that is evaluated. Source.

So if let can be used to match any enum value:

enum Foo {
    Bar,
    Baz,
    Qux(u32)
}

fn main() {
    // Create example variables
    let a = Foo::Bar;
    let b = Foo::Baz;
    let c = Foo::Qux(100);

    // Variable a matches Foo::Bar
    if let Foo::Bar = a {
        println!("a is foobar");
    }

    // Variable b does not match Foo::Bar
    // So this will print nothing
    if let Foo::Bar = b {
        println!("b is foobar");
    }

    // Variable c matches Foo::Qux which has a value
    // Similar to Some() in the previous example
    if let Foo::Qux(value) = c {
        println!("c is {}", value);
    }

    // Binding also works with `if let`
    if let Foo::Qux(value @ 100) = c {
        println!("c is one hundred");
    }
}
 

Output

a is foobar
c is 100
c is one hundred

Conclusion

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