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c++classtemplatesvisual-c++return-type

Returning value of type defined in a class template

I'm new to C++ and trying to return a value from the size() member of my X class; the return type must be of X::size_type.

template <class T> class X {
public:
    typedef size_t size_type;
    size_type size() const;
    // ...
}

template <class T> X<T>::size_type X<T>::size() const {
    // ...
}

The above code results in errors. I added typename before X<T>::size_type and the issue seems to be fixed but I don't understand why...

Is this the right way?

Solution

  • Due to the complex and sometimes ambiguous syntax of C++, sometimes hints are needed for the parser/compiler.

    In general when referring to types defined inside a class, typename is needed to hint the compiler that you're talking about a type and not a value (since X<T>::size_type can be either).