Variables in Rust

Published on November 18th, 2019

rust icon

I’ve recently started learning rust and reading “Rust the programming language” book, so I wanted to share some useful things from it.

To declare variable you’ll need to use let keyword. Because Rust is statically typed language, compiler must know types of all variables at compile time. You can specify types manually, but you don’t need to because Rust can figure them out by itself most of the time.

let number = 2;

Mutability

By default all variables in Rust are immutable. If you try to reassign them, compiler will throw an error.

number = 3;

But if you add mut keyword to variable declaration, it’ll become mutable and previous expression will be valid.

let mut number = 2;

Shadowing

In Rust you can declare new variable with same name that will shadow the old one. Once you think about it, how is this different from just using mutable variable?

Mutable variables must have same type and these can but don’t need to.

let number = false;