Error code E0562
impl Trait
is only allowed as a function return and argument type.
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
appears in a function signature.
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 the reference for more details on impl Trait
.