Rust Mutability
By default, values in variables are immutable. This is one of many nudges Rust gives you to write your code in a way that takes advantage of the safety and easy concurrency that Rust offers. However, you still have the option to make your variables mutable.
When a variable is immutable, once a value is bound to a name, you can’t change that value. The Rust compiler guarantees that when you state that a value won’t change, it really won’t change, so you don’t have to keep track of it yourself.
But mutability can be very useful, and can make code more convenient to write.
Although variables are immutable by default, you can make them mutable by adding mut in front of the variable name.
Adding mut also conveys intent to future readers of the code by indicating that other parts of the code will be changing this variable’s value.