Shadowing

Shadowing lets you declare a new variable with the same name as a previous one using let again. The new declaration replaces the old binding within its scope.

Basic shadowing

fn main() {
    let x = 5;
    let x = x + 1;   // shadows the first x, now 6
    let x = x * 2;   // shadows again, now 12
    println!("{}", x); // 12
}

Each let creates a brand new variable, so the value can be transformed step by step.

Changing the type

Because shadowing creates a new variable, you can even change the type while keeping the name.

fn main() {
    let spaces = "   ";          // &str
    let spaces = spaces.len();   // usize
    println!("{}", spaces);      // 3
}

This would not work with mut, since a mutable variable cannot change its type.

Shadowing vs mut

• mut: same variable, value changes, type stays the same.
• Shadowing: a new variable each time, type can change.

Shadowing is useful for transforming a value while reusing a meaningful name.