Variables

Rust provides type safety via static typing. Variable bindings are made with let:

# // Copyright 2023 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
fn main() {
    let x: i32 = 10;
    println!("x: {x}");
    // x = 20;
    // println!("x: {x}");
}

• Uncomment the x = 20 to demonstrate that variables are immutable by default. Add the mut keyword to allow changes.

• Warnings are enabled for this slide, such as for unused variables or unnecessary mut. These are omitted in most slides to avoid distracting warnings. Try removing the mutation but leaving the mut keyword in place.

• The i32 here is the type of the variable. This must be known at compile time, but type inference (covered later) allows the programmer to omit it in many cases.