Class is_convertible

tinyformat.h:185–211

// Test whether type T1 is convertible to type T2
template <typename T1, typename T2>
struct is_convertible
{
    private:
        // two types of different size
        struct fail { char dummy[2]; };
        struct succeed { char dummy; };
        // Try to convert a T1 to a T2 by plugging into tryConvert
        static fail tryConvert(...);
        static succeed tryConvert(const T2&);
        static const T1& makeT1();
    public:
#       ifdef _MSC_VER
        // Disable spurious loss of precision warnings in tryConvert(makeT1())
#       pragma warning(push)
#       pragma warning(disable:4244)
#       pragma warning(disable:4267)
#       endif
        // Standard trick: the (...) version of tryConvert will be chosen from
        // the overload set only if the version taking a T2 doesn't match.
        // Then we compare the sizes of the return types to check which
        // function matched.  Very neat, in a disgusting kind of way :)
        static const bool value =
            sizeof(tryConvert(makeT1())) == sizeof(succeed);
#       ifdef _MSC_VER
#       pragma warning(pop)
#       endif
};


// Detect when a type is not a wchar_t string