Question

I was wondering if there could be any way to write a template function in an abstract class, and have it (the template function) automatically instantiated with the type of the derived class?

So you have a class that looks something like this

class A
{
  virtual template < typename T>
  void vtfunc(void)
};
class B : public A
{
  /// No declared members pertaining to this example
}

Then, whenever a class derived from A is declared, it compiles “vtfunc” with itself as the template parameter T.
Then, calling vtfunc() through an interface of A calls the isntance of that function compiled for its derived class B.

Is there any way of doing this, or writing something fiddley that have this effect?

Obviously I am aware that the template parameter could only affect the internals of the class, and not the return type and parameters – they would need to be the same because of the way polymorphism works.

Answer 1

I’m not sure what you’re after but one common pattern is the so-called curiously recurring template pattern; here, the base class itself is the template, not its member functions. In other words:

template <typename T>
class A 
{ 
    virtual void vtfunc(void) 
};

class B : public A<B>
{
    …
};