Variable shadowing in Rust

Introduction

Variable shadowing lets you reuse the same name for a new variable. It helps keep your code simple and clear without making new names.

When you want to change a variable's value but keep the same name.

When you want to convert a variable's type but keep the name.

When you want to update a variable step-by-step in a calculation.

When you want to limit a variable's scope to a smaller block.

When you want to avoid creating many different variable names.

Syntax

Rust

let x = value1;
let x = value2;  // shadows previous x

Shadowing uses let again with the same variable name.

The new variable replaces the old one in the current scope.

Examples

This example adds 1 to x by shadowing it with a new value.

Rust

let x = 5;
let x = x + 1;
println!("{}", x);

This example changes spaces from a string to a number using shadowing.

Rust

let spaces = "   ";
let spaces = spaces.len();
println!("{}", spaces);

This example shows shadowing inside a smaller block, keeping outer x unchanged.

Rust

let x = 10;
{
    let x = 20;  // shadows outer x only inside this block
    println!("{}", x);
}
println!("{}", x);

Sample Program

This program shows how variable shadowing works in Rust. We reuse the name x to hold new values in the same and inner scopes.

Rust

fn main() {
    let x = 5;
    println!("First x: {}", x);

    let x = x + 10;  // shadowing x
    println!("Second x: {}", x);

    {
        let x = x * 2;  // shadowing inside block
        println!("Inner block x: {}", x);
    }

    println!("Outer x after block: {}", x);
}

Important Notes

Shadowing is different from mutability. Shadowing creates a new variable, mutability changes the same variable.

You can shadow a variable with a different type, which mutability does not allow.

Shadowing helps keep code clean by reusing names without confusion.

Summary

Variable shadowing lets you reuse the same name for a new variable.

It helps update values or change types without new names.

Shadowing works in the same or inner scopes, replacing the old variable.