Can not access member type from base-class when compiled using c++17 [duplicate]

Answer 1

When the base class B class depends upon the template parameters, even though derived class D here type alias AbcData inherited from the B, using simply AbcData in D class, is not enough.

You need to be explicit, from where you have it

template<typename ...Args>
class D : public B<float, Args...>
{
public:
    typename B<float, Args...>::AbcData m_abc; // --> like this
};