Derived template member functions cannot be converted to template member functions of the base class error

Question

Code works on (GCC5, c++14, ubuntu16) but doesn't work on (GCC7, c++14 ubuntu18) .

Could anyone can help ?

/workspace/c++/test/test/test.cpp:233:51: error: expected primary-expression before '>' token OtherT s = d->cast.template d->cast<OtherT>() ;
/workspace/c++/test/test/test.cpp:233:53: error: expected primary-expression before ')' token  OtherT s = d->cast.template d->cast<OtherT>() ;

#include<iostream>

template<typename T>
class Base
{
public:
    template<typename OtherT>
    OtherT cast() const 
    {
        OtherT a;
        T b;
        std::cout << "base" << std::endl; 
        return a;
    }    
};

template<typename T>
class Derived : public Base<T>
{
public:
    template<typename OtherT>
    OtherT cast() const
    {
        // using base = Base<T>;
        // using base::cast<OtherT>;
        auto d = (static_cast<Base<T>* >(this));
      
        OtherT s = d->cast.template d->cast<OtherT>() ;
        return s;
        // return d.template Base<T>::cast<OtherT>();
    }
};

int main()
{
    Derived<float>  der;
    return 0;
}

Answer 1

cast is a template function, so you need to explicitly specify the template keyword

OtherT s = d-> template cast<OtherT>();
//             ^^^^^^^^

Also, you don't need d->cast.template d, d is already Base<T>*.