Blocks and Scopes

Bloques

A block in Rust contains a sequence of expressions, enclosed by braces {}. 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}");
}

Si la última expresión termina con ;, el tipo y el valor resultante será ().

Ámbitos y Shadowing

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

Puedes sombrear variables, tanto las de ámbitos externos como las del propio ámbito:

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}");
}
This slide should take about 10 minutes.
  • Puedes mostrar cómo cambia el valor del bloque cambiando su última línea. Por ejemplo, añade o quita un punto y coma, o utiliza la expresión return.
  • Show that a variable’s scope is limited by adding a b in the inner block in the last example, and then trying to access it outside that block.
  • Shadowing is different from mutation, because after shadowing both variable’s memory locations exist at the same time. Both are available under the same name, depending where you use it in the code.
  • A shadowing variable can have a different type.
  • Al principio, el sombreado no es fácil, pero resulta útil para conservar valores después de .unwrap().