This library adds the optional_filter which is provided for all [Iterators][Iterator] by the [IteratorOptionalFilterExt] extension trait.
The optional_filter takes an Option<fn(&item) -> bool>, which allows for easy conditional filtering.
This however comes at a performance cost compared to a normal [filter][Iterator::filter] or the inner [Iterator] by itself.
But it is generally faster than a Box<dyn Iterator>.
See examples on the optional_filter method.