Should get an error about not being mutable

[calvin]

I have this code:

pub fn run(){
    let name = "Calvin";
    let age = 48;
    
    let age = 49;
    println!("My name is {} and today is my birthday and I am now {}", name, age);
}

It runs fine without any errors but should it not give me an error about age not being mutable? Aren't variables immutable by default?

[naim]

That is called shadowing, the first variable named age and the second variable named age are actually not the same one.
The second assignment would be a mutation if it didn't start with the let keyword.

This would be an attempt to mutate age:

pub fn run(){
    let name = "Calvin";
    let age = 48; // mut is required for this to compile
    
    age = 49;
    println!("My name is {} and today is my birthday and I am now {}", name, age);
}

Related: What is the usage of variable shadowing

[calvin]

Thank you very much clear explanation