This commit adds an IsGenericValue meta function to match arbitrary
instantiations of the GenericValue template (or derived classes).
This meta function is used in the SFINAE-checks to avoid matching
the generic APIs (operator=,==,!=; AddMember, PushBack) for instances
of the main template. This avoids ambiguities with the GenericValue
overloads.
In order to match GenericValue and its derived classes for the
SFINAE-implementation of some of the operators/functions, this
meta-function matches all types equal to or derived from a given
class. See std::is_base_of<B,D> available in C++11.
Define RAPIDJSON_HAS_CXX_TYPETRAITS to use the C++11 implementation.
Some (older) compilers have problems with compile-time constants.
This commit simplifies the implementation of the helper classes
in order to improve compiler support, especially be removing the
need of partial template specialisation.
No functional changes.
