Rust Variable Binding Declaration

Introduction

In this lab, we see an example of declaring variable bindings first and initializing them later in Rust programming language.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

Declare first

It's possible to declare variable bindings first, and initialize them later. However, this form is seldom used, as it may lead to the use of uninitialized variables.

fn main() {
    // Declare a variable binding
    let a_binding;

    {
        let x = 2;

        // Initialize the binding
        a_binding = x * x;
    }

    println!("a binding: {}", a_binding);

    let another_binding;

    // Error! Use of uninitialized binding
    println!("another binding: {}", another_binding);
    // FIXME ^ Comment out this line

    another_binding = 1;

    println!("another binding: {}", another_binding);
}

The compiler forbids use of uninitialized variables, as this would lead to undefined behavior.

Summary

Congratulations! You have completed the Declare First lab. You can practice more labs in LabEx to improve your skills.