E0515.md

A reference to a local variable was returned.

Erroneous code example:

fn get_dangling_reference() -> &'static i32 {
    let x = 0;
    &x
}

use std::slice::Iter;
fn get_dangling_iterator<'a>() -> Iter<'a, i32> {
    let v = vec![1, 2, 3];
    v.iter()
}

Local variables, function parameters and temporaries are all dropped before the end of the function body. A returned reference (or struct containing a reference) to such a dropped value would immediately be invalid. Therefore it is not allowed to return such a reference.

Consider returning a value that takes ownership of local data instead of referencing it:

use std::vec::IntoIter;

fn get_integer() -> i32 {
    let x = 0;
    x
}

fn get_owned_iterator() -> IntoIter<i32> {
    let v = vec![1, 2, 3];
    v.into_iter()
}