Support constexpr tuple members where/when required

[andrewcorrigan]

#30 is back due to e92ff99

So it looks like the destructor cannot be deleted? How about my original suggestion of __TUPLE_ANNOTATION_DESTRUCTOR, which is the same as __TUPLE_ANNOTATION but without constexpr?

[jaredhoberock]

constexpr should be gone now. It doesn't really make sense to attempt to fold it into __TUPLE_ANNOTATION, because not everything is supposed to be constexpr. I tried to apply constexpr piecemeal, but it looked like a lot of work to figure out under what conditions it needs to be applied. So I just eliminated it for now.

[andrewcorrigan]

Thanks for the quick response. However, I was kind of hoping it might be possible to figure out how to make it work, since I think it would be really valuable -- I have a ton of code that theoretically could be made constexpr.

You said you applied it piecemeal, but I naively tried keeping constexpr applied everywhere except the destructor, and that appears to be working in my code at least at a basic level. Did even that fail for you?

[jaredhoberock]

Many of std::tuple's members are constexpr only in C++14 or better: http://en.cppreference.com/w/cpp/utility/tuple/tuple

It looks like the constructor alone has 18 different versions. Making sense of all that just seems like it will require more effort than I'm prepared to expend right now.

[andrewcorrigan]

That list of constructors is intimidating... Anyway, thanks again.

[jaredhoberock]

We can leave this open to track the issue.

[andrewcorrigan]

Oh great, I thought you were implying this was "wontfix". I'll be testing it with constexpr in C++14, and will report any issues I encounter here.