Add __declspec(empty_bases) to integer_arithmetic and floating_point_arithmetic

[mathysie]

In our implementation of type_safe we use __declspec(empty_bases) as an optimalisation. The result is that the size of the resulting struct is equal to the size of an int or double or anything we want to make type_safe. For example:

template<typename T>
struct __declspec(empty_bases) CIntStrongType : type_safe::strong_typedef<T, int>,
												type_safe::strong_typedef_op::equality_comparison<T>,
												type_safe::strong_typedef_op::relational_comparison<T>,
												type_safe::strong_typedef_op::mixed_relational_comparison<T, int>,
												type_safe::strong_typedef_op::unary_plus<T>,
												type_safe::strong_typedef_op::unary_minus<T>,
												type_safe::strong_typedef_op::addition<T>,
												type_safe::strong_typedef_op::subtraction<T>,
												type_safe::strong_typedef_op::multiplication<T>,
												type_safe::strong_typedef_op::division<T>,
												type_safe::strong_typedef_op::modulo<T>,
												type_safe::strong_typedef_op::increment<T>,
												type_safe::strong_typedef_op::decrement<T>
{
	using type_safe::strong_typedef<T, int>::strong_typedef;
};
static_assert(sizeof(CIntStrongType<struct TestType>) == sizeof(int));

However, the structs floating_point_arithmetic and integer_arithmetic do not have __declspec(empty_bases). Therefore, if we would replace some structs with integer_arithmetic the implementation would be

template<typename T>
struct __declspec(empty_bases) CIntStrongType2 : type_safe::strong_typedef<T, int>,
												type_safe::strong_typedef_op::equality_comparison<T>,
												type_safe::strong_typedef_op::relational_comparison<T>,
												type_safe::strong_typedef_op::mixed_relational_comparison<T, int>,
												type_safe::strong_typedef_op::integer_arithmetic<T>
{
	using type_safe::strong_typedef<T, int>::strong_typedef;
};
static_assert(sizeof(CIntStrongType2<struct TestType>) > sizeof(int));

which uses more memory than the first version, while it has the same implementation.

Is it possible to add __declspec(empty_bases) to structs to enhance optimization?

[foonathan]

That seems to be a good idea. Please do a PR, as I don't have access to MSVC to test it out.

[mathysie]

Thanks! I'll create a PR in due time. I think I'll do it in my Christmas break