CODEWITHSUNDEEP
c++templatesstaticinitialization
Jamin Grey
Jamin Grey

Reputation: 10487

Initialize a templated class's static member that uses a template argument as the type?

I have:

template<typename TypeA, typename TypeB>
class MyClass
{
     public:
     static TypeA StaticA;
     static TypeB StaticB;

     //...other stuff....
};

How do I initialize 'StaticA' (and StaticB)?

If I do this: (in the header file, under the class's declaration but not inside it)

template<>
typename MyClass<TypeA, TypeB>::TypeA MyClass<TypeA, TypeB>::StaticA = TypeA();

Gives me:

'TypeA' was not declared in this scope.
'TypeB' was not declared in this scope.
template argument 1 is invalid
template argument 2 is invalid

And this:

template<typename TypeA, typename TypeB>
typename MyClass<TypeA, TypeB>::TypeA MyClass<TypeA, TypeB>::StaticA = TypeA();

Gives me:

conflicting declaration 'typename MyClass<TypeA, TypeB>::TypeA MyClass<TypeA, TypeB>::StaticA'
'MyClass<TypeA, TypeB>::StaticA' has a previous declaration as 'TypeA MyClass<TypeA, TypeB>::StaticA'
declaration of 'TypeA MyClass<TypeA, TypeB>::StaticA' outside of class is not definition [-fpermissive]

What's the proper way to initialize a templated class's static member that uses a template argument as the type?

Upvotes: 2

Views: 331

Answers (1)

Jamin Grey
Jamin Grey

Reputation: 10487

Ah, the correct syntax is:

template<typename TypeA, typename TypeB>
TypeA ResourceFactory<TypeA, TypeB>::StaticA = TypeA();

Which in my original problem is:

template<typename TypeA, typename TypeB>
typename MyClass<TypeA, TypeB>:: TypeA MyClass<TypeA, TypeB>::StaticA = TypeA();
^remove^ ^-------remove--------^

I was getting confused because of all the template arguments. =)

Similar to, but not entirely overlapping, this question's answer.

Upvotes: 2

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