This implements the trait for vector iterators, replacing the reverse
iterator types. The methods will stay, for implementing the future
reverse Iterable traits and convenience.
This can also be trivially implemented for circular buffers and other
variants of arrays like strings and `SmallIntMap`/`SmallIntSet`.
The `DoubleEndedIterator` trait will allow for implementing algorithms
like in-place reverse on generic mutable iterators.
The naming (`Range` vs. `Iterator`, `Bidirectional` vs. `DoubleEnded`)
can be bikeshedded in the future.
flat_map_ produces an iterator that maps each element to an iterator,
and yields the elements of the produced iterators.
This is the monadic bind :: M a -> (a -> M b) -> M b for iterators.
Named just like the vec method, but with a trailing underline until the
method resolution bug is resolved.
We discussed the name chain_map, but I decided to go with flat_map_ for consistency with vec.
Since it.map(f).flatten() would be the same as it.flat_map(f), we could choose
to just implement a flatten method instead. Either way the possibilities are the same but flat_map is more convenient.
flat_map_ produces an iterator that maps each element to an iterator,
and yields the elements of the produced iterators.
This is the monadic bind :: M a -> (a -> M b) -> M b for iterators.
Named just like the vec method, but with a trailing underline until the
method resolution bug is resolved.
The removed test for issue #2611 is well covered by the `std::iterator`
module itself.
This adds the `count` method to `IteratorUtil` to replace `EqIter`.
Fix a laundry list of warnings involving unused imports that glutted
up compilation output. There are more, but there seems to be some
false positives (where 'remedy' appears to break the build), but this
particular set of fixes seems safe.
