Please add support for std::optional

[eyjohn]

I appreciate that there is already an issue for c++17 (#2206), but I was hoping that reducing the scope to a specific component of it: std::optional would make it easier to add earlier.

This would of course mean that it will not be fully supported, e.g. no emplace until things like variadic template parameters are implemented. However I think most of the useful functionality here: https://en.cppreference.com/w/cpp/utility/optional can already be supported.

[jjerphan]

@eyjohn: FYI, #4225 introduced some support for std::optional.

[da-woods]

FYI, #4225 introduced some support for std::optional.

#4225 is not quite the same: it's using std::optional internally to try to make C++ objects behave more like Python objects (so that they're only initialized at their first use, that kind of thing). It probably ends up providing a lot of the functionality that people would try to use std::optional for, but you should view it as a feature that happens to be implemented with std::optional rather than a way of exposing std::optional.

So PRs remain welcome for a .pxd wrapper for std::optional - the basics should probably be fairly straight-forward to write.

[isVoid]

Thank you very much for making this feature available! Is it possible to backport this to 0.29?

[da-woods]

Is it possible to backport this to 0.29?

No. We really aren't backporting new features to 0.29.

However, the pxd files for the C++ standard library don't do anything special. You can just download https://github.com/cython/cython/blob/master/Cython/Includes/libcpp/optional.pxd and use it in your project.