move_semantics1.rs

[Kaiskii]

Hello, I am on move_semantics1.rs and this was the solution I came to:

// TODO: Fix the compiler error in this function.
fn fill_vec(mut vec: Vec<i32>) -> Vec<i32> {
    vec.push(88);

    vec
}

Since the TODO was to just fix the compiler error, I was assuming that this is fine, but when I checked out the solution, it uses the shadowing concept instead. Which makes it so that the vec param passed in won't be considered mutable and instead it has the let vec be mutable.

fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
    let mut vec = vec;
    //  ^^^ added

    vec.push(88);

    vec
}

While I understand that the two solutions are different, I am having a hard time understanding the situation where you would want to shadow the vec instead of having it be mutable in params since it's more straightforward to do so.

[mo8it]

This exercise demonstrates that you can declare something as mutable when you own it, even if it was immutable.

move_semantics3 recommends exactly what you did by adding mut to the parameter. This is the idiomatic way.

[Kaiskii]

Neat, thanks for explaining that this concept was later explained in a separate exercise!