The Ultimate Guide to Rust Programming/

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Let Without Assignment

Let Without Assignment

We'll cover the following...

So far, we’ve immediately assigned values to variables with let. However, it’s valid in Rust to separate these steps out. For example:

Rust 1.40.0
fn main() {
    let x;
    x = 5;
    println!("x == {}", x);
    let mut y;
    y = 5;
    y += 1;
    println!("y == {}", y);
}

I point this out now because it may be surprising that:

  • x is an immutable variable

  • But we’re allowed to say x = 5 ...