Blocks and Scopes

Blocks

A block in Rust contains a sequence of expressions. Each block has a value and a type, which are those of the last expression of the block:

fn main() {
    let z = 13;
    let x = {
        let y = 10;
        println!("y: {y}");
        z - y
    };
    println!("x: {x}");
}

If the last expression ends with ;, then the resulting value and type is ().

Scopes and Shadowing

A variable’s scope is limited to the enclosing block.

You can shadow variables, both those from outer scopes and variables from the same scope:

fn main() {
    let a = 10;
    println!("before: {a}");
    {
        let a = "hello";
        println!("inner scope: {a}");

        let a = true;
        println!("shadowed in inner scope: {a}");
    }

    println!("after: {a}");
}