pub unsafe trait TrustedLen: Iterator { }
🔬This is a nightly-only experimental API. (trusted_len #37572)
Expand description

An iterator that reports an accurate length using size_hint.

The iterator reports a size hint where it is either exact (lower bound is equal to upper bound), or the upper bound is None. The upper bound must only be None if the actual iterator length is larger than usize::MAX. In that case, the lower bound must be usize::MAX, resulting in an Iterator::size_hint() of (usize::MAX, None).

The iterator must produce exactly the number of elements it reported or diverge before reaching the end.


This trait must only be implemented when the contract is upheld. Consumers of this trait must inspect Iterator::size_hint()’s upper bound.