Question

Here is code sample which reproduces my problem:

template <typename myType>
class Base {
public:
    Base() {}
    virtual ~Base() {}
protected:
    int myOption;
    virtual void set() = 0;
};

template <typename InterfaceType>
class ChildClass : public Base < std::vector<InterfaceType> >
{
public:
    ChildClass() {}
    virtual ~ChildClass() {}
 protected:
    virtual void set();
};

template <typename InterfaceType>
void ChildClass<InterfaceType>::set()
{
     myOption = 10;
}

My usage in main():

ChildClass<int> myObject;

I get the following error (gcc 4.4.3 on ubuntu):

‘myOption’ was not declared in this scope

If my ChildClass would be without new template parameter this would work fine, i.e.:

class ChildClass : public Base < std::vector<SomeConcreteType> >

---

Edit

I’ve managed to solve it, if my set method looks like:

Base<std::vector<InterfaceType> >::myOption = 10;

It works fine. Still though not sure why I need to specify all template parameters.

Answer 1

myOption is not a dependent name, i.e. it doesn’t depend on the template arguments explicitly so the compiler tries to look it up early. You must make it a dependent name:

template <typename InterfaceType>
void ChildClass<InterfaceType>::set()
{
     this->myOption = 10;
}

Now it depends on the type of this and thus on the template arguments. Therefore the compiler will bind it at the time of instantiation.

This is called Two-phase name lookup.