Detect C++03-style metafunctions

[akrzemi1]

A common pattern in C++03 is to declare meta-functions (type traits) via classes and specializations derived from true_type or integral_constant<bool, ...>. Like:

template <typename MVP, typename = void>
struct check_safe_dual_storage_exception_safety : ::std::true_type {};

template <typename MVP>
struct check_safe_dual_storage_exception_safety<MVP, typename MVP::is_safe_dual_storage_mark_policy>
: std::integral_constant<bool, AK_TOOLKIT_IS_NOEXCEPT(typename MVP::representation_type(MVP::marked_value()))>
{
};

(https://github.com/akrzemi1/markable/blob/master/include/ak_toolkit/markable.hpp#L236-243)

It would be very useful if MrDocs were able to identify this as an idiom (even with the help of some marking) and express it more directly in the rendered docs.

Is this even possible?

[alandefreitas]

We use a pattern like this in Boost.URL:

namespace detail {
template <typename X, typename = void>
struct my_trait_impl : ::std::true_type {};

template <typename X>
struct my_trait_impl<X, typename /* ... */>
: /* ... */
{
};
}

template <typename X>
using my_trait = detail::my_trait_impl<X>;

or

template <typename X>
struct my_trait : detail::my_trait_impl<X> {};