Support using better-enum as key in dictionaries and maps.

[svnscha]

Thanks for better-enum. It is awesome. However I was missing a feature to use the enum values in unordered_map. I have extended it for this use case. Please review and accept my PR.

int main()
{
	Channel channel = Channel::Red;
	
	std::unordered_map<Channel, int> u = {
		{Channel::Red, 1},
		{Channel::Blue, 3},
	};

	printf("Red %d\n", u[Channel::Red]);
	printf("Blue %d\n", u[Channel::Blue]);

	return 0;
}

[svnscha]

My previous attempt does not work and I totally did not think about that situation that a better enum could be in a namespace. Then the specialization does fail.

However, how about that approach?

namespace test {

BETTER_ENUM(Channel, char, Red = 1, Green, Blue)

}

BETTER_ENUMS_DECLARE_STD_HASH(test::Channel)

int main()
{
	test::Channel channel = test::Channel::Red;
	
	std::unordered_map<test::Channel, int> u = {
		{test::Channel::Red, 1},
		{test::Channel::Blue, 3},
	};

	printf("Red %d\n", u[test::Channel::Red]);
	printf("Blue %d\n", u[test::Channel::Blue]);

	return 0;
}

[aantron]

This check shouldn't be necessary.

[svnscha]

Yup, will handle that.

[aantron]

Why use the index rather than the value? _to_index runs a loop internally, whereas _to_integral is just a cast. Is this deliberate?

[svnscha]

Yes indeed. I am going to update that to use _to_integral.

[aantron]

However, how about that approach?

If it works, I will merge it :)

If possible, can you add a test case that exercises this? It should probably go somewhere in this block:

better-enums/test/cxxtest/general.h

Lines 30 to 32 in 8a0d376

	// Using BETTER_ENUMS_HAVE_CONSTEXPR_ as a proxy for C++11 support. This should
	// be changed to be more precise in the future.
	#ifdef BETTER_ENUMS_HAVE_CONSTEXPR_

[svnscha]

However, how about that approach?

If it works, I will merge it :)

If possible, can you add a test case that exercises this? It should probably go somewhere in this block:

better-enums/test/cxxtest/general.h

Lines 30 to 32 in 8a0d376

	// Using BETTER_ENUMS_HAVE_CONSTEXPR_ as a proxy for C++11 support. This should
	// be changed to be more precise in the future.
	#ifdef BETTER_ENUMS_HAVE_CONSTEXPR_

Do you mean by making a test case that tests the unordered_map?

[aantron]

Do you mean by making a test case that tests the unordered_map?

Yes.

[svnscha]

I am going to add the test case on Monday.

[svnscha]

I have added a new runtime test @aantron as I dont know if it is really possible to make a std::hash operator usable in a constexpr. Would you chheck it out and see if that is how you wanted it?

[aantron]

A run-time test is fine. It looks like it's not compiling, though. See, e.g., https://travis-ci.org/aantron/better-enums/jobs/558780607#L1386.

[svnscha]

Wow, finally.. @aantron ^^

[aantron]

:p

Thanks!