2 Checks for items that implement `.len()` but not
6 It is good custom to have both methods, because for
7 some data structures, asking about the length will be a costly operation,
8 whereas `.is_empty()` can usually answer in constant time. Also it used to
9 lead to false positives on the [`len_zero`](#len_zero) lint – currently that
10 lint will ignore such entities.
15 pub fn len(&self) -> usize {