Cannot access type alias from class template definition in separate file without typing full declaration of alias type

Question

I have a class template like Sample.hpp with type alias X.

#ifndef SAMPLE_HPP
#define SAMPLE_HPP

template<typename STA, typename STB>
class Sample
{
    using X = Sample<STA,STB>;

public:
    Sample();
    inline X* GetNext() const;

private:
    X* Next;
};

#include "Sample.cpp"

#endif // SAMPLE_HPP

And definitions are in Sample.cpp.

#include "Sample.hpp"

template<typename STA, typename STB>
Sample<STA,STB>::Sample() {
    Next = nullptr;
}

template<typename STA, typename STB>
typename Sample<STA,STB>::X* Sample<STA,STB>::GetNext() const {
    return this->Next;
}

My question is that, are there any others ways of defining GetNext function. For example without typename or without full declaration of Sample class template. When I change code to

template<typename STA, typename STB>
Sample<STA,STB>* Sample<STA,STB>::GetNext() const {
    return this->Next;
}

It works, but I cant use type alias here directly , for example :

template<typename STA, typename STB>
X* Sample<STA,STB>::GetNext() const {
    return this->Next;
}

Rakete1111 · Accepted Answer · 2017-09-21 17:24:20Z

5

You can use a trailing return type with the help of auto:

template<typename STA, typename STB>
auto Sample<STA, STB>::GetNext() const -> X* {
    return this->Next;
}

answered Sep 21, 2017 at 17:24

Rakete1111

49.5k19 gold badges133 silver badges173 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Cherkesgiller Over a year ago

Thank you very much, can you please explain this in more detail?

Rakete1111 Over a year ago

@CherkesgillerTural Sure thing. So if you put X* at the start, the compiler has no way of knowing that X is supposed to be, so you get an error. But if you write it after, then the compiler can look in the scope of Sample<STA, STB> for X. If you put it before, it didn't encounter Sample<STA, STB> yet, so it can't look for X there. More information about that here.

Cherkesgiller Over a year ago

Thank you very much, @Rakete111.

Collectives™ on Stack Overflow

Cannot access type alias from class template definition in separate file without typing full declaration of alias type

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related