rust/example/gen_block_iterate.rs

// Copied from https://github.com/rust-lang/rust/blob/46455dc65069387f2dc46612f13fd45452ab301a/tests/ui/coroutine/gen_block_iterate.rs
// revisions: next old
//compile-flags: --edition 2024 -Zunstable-options
//[next] compile-flags: -Ztrait-solver=next
// run-pass
#![feature(gen_blocks)]

fn foo() -> impl Iterator<Item = u32> {
    gen { yield 42; for x in 3..6 { yield x } }
}

fn moved() -> impl Iterator<Item = u32> {
    let mut x = "foo".to_string();
    gen move {
        yield 42;
        if x == "foo" { return }
        x.clear();
        for x in 3..6 { yield x }
    }
}

fn main() {
    let mut iter = foo();
    assert_eq!(iter.next(), Some(42));
    assert_eq!(iter.next(), Some(3));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), Some(5));
    assert_eq!(iter.next(), None);
    // `gen` blocks are fused
    assert_eq!(iter.next(), None);

    let mut iter = moved();
    assert_eq!(iter.next(), Some(42));
    assert_eq!(iter.next(), None);

}