> how does it even implement a len() which has the behavior in the article? It's from `ExactSizedIterator.len()` and is a specialization of the case where `Ite

> how does it even implement a len() which has the behavior in the article? It's from `ExactSizedIterator.len()` and is a specialization of the case where `Iterator.size_hint()` returns known to be correct values. It's a bit confusing on `Range<>` as it's not the distance between start/end or anything like that (well it's the number of steps when iterating Range so kinda the distance). It also has the side-effect that it's not implemented for Range<u64> as I guess not to hinder 32bit compatibility (len/size_hint return a usize). Because it's the iteration length it also is calculated based on iterations criteria, simplified `if start < end { end- start } else { 0 }`. Except in practice it goes from `len` to `size_hint` to the `Steps.steps_between` API in-lining all the calls and optimizing away the unnecessary overhead.