[libcxx-commits] [libcxx] [libc++] `std::views::split`: fix handling of empty ranges (LWG4017) (PR #87916)

[Jan Kokemüller via libcxx-commits]

jiixyj wrote:

I'm thinking about an alternative design, where:

- `optional` is not used
- the `trailing_empty_` boolean is repurposed as `has_more_`, which is true if and only if the `split_view` has more elements
- all constructors of the `iterators` returned from the `begin()` function of the `split_view` stay as they are -- with the semantics, that if constructed with an "end" iterator, they will still return one empty range.
- the `end()` function of the `split_view` will call new constructor overload(s) of `iterator` as needed. Those constructor overloads are libc++ vendor extensions.

This has the following advantages:

- `optional` machinery is not pulled in
- the data layouts stay exactly the same
- the currently specified iterator constructor overloads are not touched

https://github.com/llvm/llvm-project/pull/87916