Summary - Variables

Combine let, mut, const and shadowing to build a counter program.

Variables summary

let creates an immutable binding; let mut a mutable one; const a compile-time constant (type required, UPPER_CASE); static a global value with a single address; shadowing a new variable with the same name (its type can change). Rust choosing immutability by default lets you see immediately which values change just by reading the code.

Multiple bindings and tuples

A tuple can be destructured with a single let to define several variables:

let (ad, yas) = ("Ada", 36);
let (mut x, y) = (1, 2);
x += y;
println!("{ad} {yas} {x}");  // Ada 36 3

Parts you won't use are skipped with _: let (_, yas) = kisi;.

Exercise All together

Define const HEDEF: i32 = 10;. In main, destructure with let (baslangic, adim) = (1, 3);, create let mut deger = baslangic; and do deger += adim; while deger < HEDEF. Print the result.

Show example solution

const HEDEF: i32 = 10;

fn main() {
    let (baslangic, adim) = (1, 3);
    let mut deger = baslangic;
    while deger < HEDEF {
        deger += adim;
    }
    println!("{}", deger);
}

Test yourself

Which compiles?
- let x = 1; let x = "bir";
- let x = 1; x = 2;
- let mut x = 1; x = "bir";
- const X = 1;
Show answer

let x = 1; let x = "bir"; — Shadowing can change the type; the others fail because of immutability, a type mismatch and a missing type, respectively.

Destructure

let ____ = (10, 20);
println!("{}", a + b);

Show answer

let (a, b) = (10, 20);
println!("{}", a + b);

Group summary

let

Immutable
let mut

Mutable
const

Compile-time constant
Shadowing

New variable, same name

Next lesson: Integers

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