move_semantics6 intended solution does not address the error

[ramenhost]

Hinted solution

rustlings/exercises/06_move_semantics/move_semantics6.rs

Lines 23 to 28 in 7105310

	// Should take ownership
	fn string_uppercase(mut data: &String) {
	data = &data.to_uppercase();
	println!("{}", data);
	}

Based on hints and code comments, the expected solution here is to make string_uppercase() take ownership of data. When done, the compiler prompts to remove & from line 25 to match the type of variable data.

Actual error

The actual error shown (before making any changes) is temporary value dropped while borrowed.

error[E0716]: temporary value dropped while borrowed
  --> exercises/06_move_semantics/move_semantics6.rs:23:13
   |
22 | fn string_uppercase(mut data: &String) {
   |                               - let's call the lifetime of this reference `'1`
23 |     data = &data.to_uppercase();
   |     --------^^^^^^^^^^^^^^^^^^^- temporary value is freed at the end of this statement
   |     |       |
   |     |       creates a temporary value which is freed while still in use
   |     assignment requires that borrow lasts for `'1`

Addressing the compiler error

The real problem here is not that string_uppercase takes reference. It i s because in line 25, a reference to temporary value is created. Since the temporary value goes out of scope after line 25, the reference out-lives the value being referred to.
If we were to follow this thread, we would end up with a solution that does not necessarily take ownership. Some examples below,

// Should take ownership
fn string_uppercase(mut data: &String) {
    let data_uc = data.to_uppercase();

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

or without another variable

// Should take ownership
fn string_uppercase(mut data: &String) {
    let data = &data.to_uppercase();

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

I understand that in main(), data is not used after calling string_uppercase() and hence it is valid solution to take ownership. However, my concern is that it does not address the root cause, rather fixes error as a side effect. As someone using rustlings to learn rust, this confused me.

Environment

@ramenhost ➜ /workspaces/rustlings (main) $ rustc --version
rustc 1.77.2 (25ef9e3d8 2024-04-09)
@ramenhost ➜ /workspaces/rustlings (main) $ rustlings --version
rustlings 5.6.1