add tuple_size to camp::array

[gberg617]

Add tuple_size to camp::array. This is needed in order to use camp::apply on arrays.

[adayton1]

There's already a tuple_size entity in array.hpp. Does that one not work?

[gberg617]

That one does not work for me because it's defined within the std namespace. camp::apply looks for camp::tuple_size, so we need to define one that specializes for camp::array.

[adayton1]

Can you move this one to array.hpp, then?

[adayton1]

I'm actually wondering if we should remove camp::array since we should be able to use std::array in device code now that we require c++17 (almost everything in std::array is constexpr in c++17, and everything is constexpr in c++20). With nvcc you have to supply the --expt-relaxed-constexpr flag, which will make all constexpr function __host__ __device__, but with amdclang, constexpr automatically implies __host__ __device__.

[gberg617]

I'm actually wondering if we should remove camp::array since we should be able to use std::array in device code now that we require c++17 (almost everything in std::array is constexpr in c++17, and everything is constexpr in c++20). With nvcc you have to supply the --expt-relaxed-constexpr flag, which will make all constexpr function __host__ __device__, but with amdclang, constexpr automatically implies __host__ __device__.

I would be fine with this. It doesn't look like it's used in RAJA, other than in my SubView PR.

[gberg617]

See #195