Propagating 'typedef' from based to derived class for 'template'

user_135960 0
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I'm trying to define base class, which contains typedef's only. 

template<typename T>
class A
{
public:
    typedef std::vector<T> Vec_t;
};


template<typename T>
class B : public A<T>
{
private:
    Vec_t v;  // fails - Vec_t is not recognized
};

Why in B I receive an error that Vec_t is not recognized and I need to write it explicitly?

typename A<T>::Vec_t v;
name-lookup templates typedef inheritance c++
7 Answers

For completeness, here's how you could mitigate this nuisance a little, either:

  • re-typedef those types in derived classes, or better - as with methods -
  • just import those names in the derived class scope with a using declaration:
template<typename T>
class A
{
public:
    typedef std::vector<T> Vec_t;
};


template<typename T>
class B : public A<T>
{
public:
    using typename A<T>::Vec_t;
    // .........

private:
    Vec_t v;
};

It can be useful if you have more than one mentioning of the inherited typedef in the derived class. Also you don't need to add typename each time with this.

user_8950770
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