Rust let 绑定的不变性

Question

I thought that let is supposed to be an immutable binding. Why does the correct code work then? (assigned a twice)

let a = [1, 2, 3, 4, 5];
println! ("{:?}", a);

let (a, b, c) = (1,2,3);
println! ("{:?}", a);
println! ("{:?}", b);
println! ("{:?}", c);

And the result of cargo run is:

Guess the number! From a 1 - 100 inclusive
[1, 2, 3, 4, 5]
1
2
3

Answer 1

Your code is more or less equivalent to this:

let first_a = [1, 2, 3, 4, 5];
println! ("{:?}", first_a);

let (second_a, b, c) = (1,2,3);
println! ("{:?}", second_a);
println! ("{:?}", b);
println! ("{:?}", c);

The second a is a completely new variable. The first a is no longer accessible once you create a second one.

Answer 2

a is being shadowed .

let a = 5;
a = 6; // not allowed

let a = 5;
let a = 6; //allowed

Bad form to do this in the same block like that.