Template specialization to use default type if class member typedef does not exist

Question

I\'m trying to write code that uses a member typedef of a template argument, but want to supply a default type if the template argument does not have that typedef. A simpli

Answer 1

You can do that by utilizing SFINAE:

template struct has_type {
    template static char (&test(typename U::Type const*))[1];
    template static char (&test(...))[2];
    static const bool value = (sizeof(test(0)) == 1);
};

template::value> struct Get_Type {
    typedef DefaultType Type;
};

template struct Get_Type { 
    typedef typename T::Type Type;
};