My Rustlings answers

move_semantics1.rs

// move_semantics1.rs
// Make me compile! Scroll down for hints :)

pub fn main() {
    let vec0 = Vec::new();

    let mut vec1 = fill_vec(vec0);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

    vec1.push(88);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

}

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

    vec.push(22);
    vec.push(44);
    vec.push(66);

    vec
}















// So you've got the "cannot borrow immutable local variable `vec1` as mutable" error on line 11,
// right? The fix for this is going to be adding one keyword, and the addition is NOT on line 11
// where the error is.

move_semantics2-1.rs

// move_semantics2.rs
// Make me compile without changing line 10! Scroll down for hints :)

pub fn main() {
    let vec0 = Vec::new();

    let mut vec1 = fill_vec(vec0.clone());

    // Do not change the following line!
    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);

    vec1.push(88);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

}

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

    vec.push(22);
    vec.push(44);
    vec.push(66);

    vec
}














// So `vec0` is being *moved* into the function `fill_vec` when we call it on
// line 7, which means it gets dropped at the end of `fill_vec`, which means we
// can't use `vec0` again on line 10 (or anywhere else in `main` after the
// `fill_vec` call for that matter). We could fix this in a few ways, try them
// all!
// 1. Make another, separate version of the data that's in `vec0` and pass that
// to `fill_vec` instead.
// 2. Make `fill_vec` borrow its argument instead of taking ownership of it,
// and then copy the data within the function in order to return an owned
// `Vec<i32>`
// 3. Make `fill_vec` *mutably* borrow its argument (which will need to be
// mutable), modify it directly, then not return anything. Then you can get rid
// of `vec1` entirely -- note that this will change what gets printed by the
// first `println!`

move_semantics2-2.rs

// move_semantics2.rs
// Make me compile without changing line 10! Scroll down for hints :)

pub fn main() {
    let vec0 = Vec::new();

    let mut vec1 = fill_vec(&vec0);

    // Do not change the following line!
    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);

    vec1.push(88);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

}

fn fill_vec(vec: &Vec<i32>) -> Vec<i32> {
    let mut vec = vec.clone();

    vec.push(22);
    vec.push(44);
    vec.push(66);

    vec
}














// So `vec0` is being *moved* into the function `fill_vec` when we call it on
// line 7, which means it gets dropped at the end of `fill_vec`, which means we
// can't use `vec0` again on line 10 (or anywhere else in `main` after the
// `fill_vec` call for that matter). We could fix this in a few ways, try them
// all!
// 1. Make another, separate version of the data that's in `vec0` and pass that
// to `fill_vec` instead.
// 2. Make `fill_vec` borrow its argument instead of taking ownership of it,
// and then copy the data within the function in order to return an owned
// `Vec<i32>`
// 3. Make `fill_vec` *mutably* borrow its argument (which will need to be
// mutable), modify it directly, then not return anything. Then you can get rid
// of `vec1` entirely -- note that this will change what gets printed by the
// first `println!`

move_semantics2-3.rs

// move_semantics2.rs
// Make me compile without changing line 10! Scroll down for hints :)

pub fn main() {
    let mut vec0 = Vec::new();

    fill_vec(&mut vec0);

    // Do not change the following line!
    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);

}

fn fill_vec(vec: &mut Vec<i32>) {
    let vec = vec;

    vec.push(22);
    vec.push(44);
    vec.push(66);
    
}














// So `vec0` is being *moved* into the function `fill_vec` when we call it on
// line 7, which means it gets dropped at the end of `fill_vec`, which means we
// can't use `vec0` again on line 10 (or anywhere else in `main` after the
// `fill_vec` call for that matter). We could fix this in a few ways, try them
// all!
// 1. Make another, separate version of the data that's in `vec0` and pass that
// to `fill_vec` instead.
// 2. Make `fill_vec` borrow its argument instead of taking ownership of it,
// and then copy the data within the function in order to return an owned
// `Vec<i32>`
// 3. Make `fill_vec` *mutably* borrow its argument (which will need to be
// mutable), modify it directly, then not return anything. Then you can get rid
// of `vec1` entirely -- note that this will change what gets printed by the
// first `println!`

move_semantics3.rs

// move_semantics3.rs
// Make me compile without adding new lines-- just changing existing lines!
// (no lines with multiple semicolons necessary!)
// Scroll down for hints :)

pub fn main() {
    let vec0 = Vec::new();

    let mut vec1 = fill_vec(vec0);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

    vec1.push(88);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

}

fn fill_vec(mut vec: Vec<i32>) -> Vec<i32> {
    vec.push(22);
    vec.push(44);
    vec.push(66);

    vec
}

















// The difference between this one and the previous ones is that the first line
// of `fn fill_vec` that had `let mut vec = vec;` is no longer there. You can,
// instead of adding that line back, add `mut` in one place that will change
// an existing binding to be a mutable binding instead of an immutable one :)

move_semantics4.rs

// move_semantics4.rs
// Refactor this code so that instead of having `vec0` and creating the vector
// in `fn main`, we instead create it within `fn fill_vec` and transfer the
// freshly created vector from fill_vec to its caller. Scroll for hints!

pub fn main() {

    let mut vec1 = fill_vec();

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

    vec1.push(88);

    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);

}

fn fill_vec() -> Vec<i32> {
    [22, 44, 66].to_vec()
}














// Stop reading whenever you feel like you have enough direction :) Or try
// doing one step and then fixing the compiler errors that result!
// So the end goal is to:
// - get rid of the first line in main that creates the new vector
// - so then `vec0` doesn't exist, so we can't pass it to `fill_vec`
// - we don't want to pass anything to `fill_vec`, so its signature should
//   reflect that it does not take any arguments
// - since we're not creating a new vec in `main` anymore, we need to create
//   a new vec in `fill_vec`, similarly to the way we did in `main`

You can comment line 15 in move_semantics2-3.rs

Assuming others will arrive here from a search engine, as I did.

Here's my solutions for 5 and 6 (comments removed for brevity's sake); 6 was confusing at first but makes sense in retrospect:

move_semantics5.rs

fn main() {
    let mut x = 100;
    let y = &mut x;
    *y += 100;
    let z = &mut x;
    *z += 1000;
    assert_eq!(x, 1200);
}

move_semantics6.rs

fn main() {
    let data = "Rust is great!".to_string();
    get_char(&data);
    string_uppercase(data);
}

fn get_char(data: &String) -> char {
    data.chars().last().unwrap()
}

fn string_uppercase(mut data: String) {
    data = data.to_uppercase();

    println!("{}", data);
}