MINIFICPP-2159 Add heterogeneous lookup to FlatMap

[martinzink]

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[szaszm]

Suggested change

	template<typename T>
	requires std::equality_comparable_with<K, T>
	bool contains(const T& key) const {
	bool contains(std::equality_comparable_with<K> auto const& key) const {

[martinzink]

good idea, changed it and the others (except for operator[]) in f209288

[martinzink]

it looks like MSVC doesnt like constraint auto, Im getting

C:\nifi-minifi-cpp\libminifi\test\unit\FlatMapTests.cpp(51): fatal error C1001: Internal compiler error.
(compiler file 'D:\a\_work\1\s\src\vctools\Compiler\CxxFE\sl\p1\c\trees.c', line 24533)
 To work around this problem, try simplifying or changing the program near the locations listed above.
If possible please provide a repro here: https://developercommunity.visualstudio.com/

I've found some reported issues with constraint auto and MSVC but those issues should be solved, ours is a bit more complex. I will try to create an MRE about this issue and file a bug with microsoft, in the meantime should I revert to explicit templates?

[szaszm]

I'd use the shortest for that's working with all targeted compilers.
That translates to first fallback to this:

  template<std::equality_comparable_with<K> T>
  bool contains(T const& key) const {

and second fallback to the original version.

On an unrelated note, we should add noexcept wherever it makes sense. It may make our life easier down the line.

[martinzink]

Good idea, the first fallback works on MSVC aswell. 617fc38
Adding noexcept where applicable is a good idea, I didnt find any obvious target on a quick glance, and I didnt want to burden this PR with a more complex analysis. Should I file a new jira for this?

[szaszm]

For noexcept, I was thinking operator[], find, erase and contains. It may need to be conditional, e.g. erase does swap, so it needs to be std::is_nothrow_swappable_v. I was hoping for noexcept find, but it would have to rely on a complex condition, so it may not be feasible after all.

If nothing obvious stands out, don't bother with the new Jira.