typedef Using a typename

Question

So I had some code that I asked a question about which I realized was confusing and later edited out:

template 
struct foo {
    typedef typename pair PointType;
private:
    PointType point;
};

I'm not certain what the function of the typename in PointType's definition is. It this keyword just omitted? I notice that it's frequently used in the using definitions to add the *_t extensions in type support. Perhaps that's what was intended here?

user_8576366 · Answer

You are using the second type of typename use, according to cppreference: http://en.cppreference.com/w/cpp/keyword/typename

Basically, you are giving a hint to the compiler: T is a template dependent type in pair

user_2204581 · Answer

It is necessary because pair is a dependent name, meaning that it changes depending on how foo was initialized.

typedef Using a typename

2 Answers