You can forward declare a template inner class inside a normal class, and use the defined type as any other forward declared type.
class Outer {
template <int N> class Inner;
typedef Inner<0> Inner0;
Inner0* f();
};
template<int N>
class Outer::Inner {};
Now if Outer is itself a template class, is there a way to keep the declaration of Inner outside the declaration of Outer ? Something like :
template<typename T>
class Outer {
template <int N> class Inner;
typedef Inner<0> Inner0;
Inner0* f();
};
template<typename T, int N> //This won't work
class Outer<T>::Inner {};
Is there a correct syntax to declare Outer with the right template parameters ?
Try the following
template<typename T>
template <int N>
class Outer<T>::Inner {};
According to the C++ Standard (14.5.2 Member templates)
1 A template can be declared within a class or class template; such a template is called a member template. A member template can be defined within or outside its class definition or class template definition. A member template of a class template that is defined outside of its class template definition shall be specified with the template-parameters of the class template followed by the template-parameters of the member template.
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