Why can't my derived class find my base class's type alias?

Question

Let\'s start with the code example, because it should be easy to see what\'s going on:

template 
struct Base
{
    using Type = int;
};

te         


        

Answer 1

because Type is a dependent name (it depends on the template Base<T>). You need to qualify it and use typename. You can also qualify it with Derived:: (as the op himself figure it out):

template<typename T>
struct Derived : public Base<T>
{
    using NewType = typename Base<T>::Type;
    // or
    using NewType2 = typename Derived::Type;
};

You can read more about dependent names here:

https://en.cppreference.com/w/cpp/language/dependent_name

How do you understand dependent names in C++

Where and why do I have to put the "template" and "typename" keywords?

Why do I have to access template base class members through the this pointer?

"not declared in this scope" error with templates and inheritance