Mutability and intro into strings¶

By default variables in immutable - once the value is bound to a name, you can't change that value.

fn main() {
    let a = 10;
    a = 20;
    println!("{}", a)
}

When compiling this program, it will throw an error saying error: re-assignment of immutable variable.

However, sometimes the mutability can become very useful, it can be added by specifying mut keyword:

fn main() {
    let mut a = 10;
    a = 20;
    println!("{}", a)
}

There is also a variable type of Constant. They are bound to a name and are not allowed to change - you cannot add the mut keyword.

Constants can be defined using const keyword, data type must be annotated. Can be defined in any scope, including the global scope.

By convention, the constant names must be defined in all caps.

const MAX:u8 = 132;
fn main() {
    let mut a = 10;
    a = 20;
    println!("{} {}", a, MAX)
}