Enable noexcept for special member functions

[pfent]

The hopscotch_hash container already was nothrow move constructible, but was missing the conditional noexcept for the default constructor, swap, and move assignment.

[Tessil]

Thanks for the PR.

It looks good but the default constructor could still throw even with DEFAULT_INIT_BUCKETS_SIZE == 0 as the Hash, KeyEqual and GrowthPolicy default constructors could potentially throw. We would need to add some check on these.

[pfent]

Thanks for the review, you raised a valid point:
The default growth policies are not trivially noexcept, so I added a small helper to help detect that the growth policies are actually noexcept when initialized with zero.

[Tessil]

Sorry for the delay.

The change looks good now, thanks.

Just a minor question, could we create a default hopscotch_hash constructor with the noexcept checks and then for the default constructors of (b)hopscotch_map/set check the noexcept of the hopscotch_hash constructor (and call it)? Mainly to avoid all the duplication of the checks.

[pfent]

Good point. I moved the checks to hopscotch_hash, which makes the overall diff a bit smaller.

[Tessil]

Thanks, looks good.

Currently the library is compatible with C++11 (it was so when designed and kept like that) but std::is_nothrow_swappable requires C++17.

I'll move the library and tests to C++17 over the weekend as there's no real reason to keep C++11 compatibility and merge the change then.

[Tessil]

I merged the changes. Note that I had to disable the test_noexcept test on MSVC as std::list is not std::is_nothrow_move_constructible in their implementation. Generally this overflow list should be empty (there need to be > 62 collisions on the same bucket for it to fill), but it's still blocking noexcept on MSVC. I have to check if there's eventually an alternative.