This program is derived from tests for BTreeSet:

use pstd::collections::BTreeSet;

fn main() {
    let s246 = BTreeSet::from([2, 4, 6]);
    let s23456 = BTreeSet::from_iter(2..=6);
    let mut iter = s246.difference(&s23456);
    assert_eq!(iter.size_hint(), (0, Some(3)));
    assert_eq!(iter.next(), None);

    let s12345 = BTreeSet::from_iter(1..=5);
    iter = s246.difference(&s12345);
    assert_eq!(iter.size_hint(), (0, Some(3)));
    assert_eq!(iter.next(), Some(&6));
    assert_eq!(iter.size_hint(), (0, Some(0)));
    assert_eq!(iter.next(), None);
}

It doesn't compile, I get an error:

error[E0597]: `s12345` does not live long enough
  --> src/main.rs:11:28
   |
10 |     let s12345 = BTreeSet::from_iter(1..=5);
   |         ------ binding `s12345` declared here
11 |     iter = s246.difference(&s12345);
   |                            ^^^^^^^ borrowed value does not live long enough
...
16 | }
   | -
   | |
   | `s12345` dropped here while still borrowed
   | borrow might be used here, when `iter` is dropped and runs the destructor for type `pstd::collections::btree_set::Difference<'_, i32, CustomTuning>`
   |
   = note: values in a scope are dropped in the opposite order they are defined

For more information about this error, try `rustc --explain E0597`.

I vaguely understand the error, and if I change the line

    iter = s246.difference(&s12345);

to

    let mut iter = s246.difference(&s12345);

the error goes away and everything is fine. What I don't understand though is that if I use std rather than pstd ( the crate I am developing ) the error also goes away. Is there some magic to suppress the error in std? What is going on?

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