Error code E0562

Abstract return types (written impl Trait for some trait Trait) are only allowed as function and inherent impl return types.

Erroneous code example:

fn main() { let count_to_ten: impl Iterator<Item=usize> = 0..10; // error: `impl Trait` not allowed outside of function and inherent method // return types for i in count_to_ten { println!("{}", i); } }

Make sure impl Trait only appears in return-type position.

fn count_to_n(n: usize) -> impl Iterator<Item=usize> { 0..n } fn main() { for i in count_to_n(10) { // ok! println!("{}", i); } }

See RFC 1522 for more details.