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Rust 1.31.0-beta.13
d4de9b138

Mutability

There is a new edition of the book and this is an old link.

Variables are immutable only by default; we can make them mutable by adding mut in front of the variable name.

let mut x = 5;
println!("The value of x is: {}", x);
x = 6;
println!("The value of x is: {}", x);Run

Here are the relevant sections in the new and old books: