Compiling error on template method, return is instance from inner class [duplicate]

Question

Here is a simplified example:

template<typename T>
class MyTemplate
{
  class Inner {};
  Inner met();
};

template<typename T>
MyTemplate<T>::Inner  MyTemplate<T>::met()
{ }

I get the following compilation error:

expected constructor, destructor, or type conversion before 'met'

I use GCC. It seems the compiler doesn't recognize MyTemplate<T>::Inner as a proper class. How can I fix this? I've tried sticking the typename keyword here and there to no avail. Right now, the only way I can manage to compile this is to inline the method definition in the class declaration, which I would like to avoid.

Answer 1

Clang reports the following:

error: missing 'typename' prior to dependent type name
'MyTemplate<T>::Inner' MyTemplate<T>::Inner  MyTemplate<T>::met()
^~~~~~~~~~~~~~~~~~~~ typename  1 error generated.

And placing typename in the appropriate place fixes it.

template<typename T>
class MyTemplate
{
  class Inner {};
  Inner met();
};

template<typename T>
typename MyTemplate<T>::Inner  MyTemplate<T>::met()
{ }

Did you put typename in the correct location? If so, then this must be a bug in G++.

Answer 2

The return type of MyTemplate::met is a dependent name, so you need to add the typename keyword before it. The following compiles on gcc-4.5.1

template<typename T>
struct MyTemplate
{
  class Inner {};
  Inner met();
};

template<typename T>
typename MyTemplate<T>::Inner  MyTemplate<T>::met()
{
  return typename MyTemplate<T>::Inner();
}

int main()
{
  MyTemplate<int> foo;

  MyTemplate<int>::Inner bar = foo.met();
}