Have a template parameter that can be pointer type or non-pointer type

Question

Suppose I have something like:

template <class T>
void do_something(T t){
  pass_it_somewhere(t);
  t->do_something();
}

Now it would be useful that T is allowed to be a pointer- or a non-pointer type. Function do_something(...) can basically handle pointers and non-pointers, except for the t->do_something(). For pointers, I would need a -> and for non-pointers, I would need a . to access members.

Is there a way to make T accept pointers and non-pointers?

Answer 1

You could create a dereference mechanism as below:

template<typename T>
std::enable_if_t<std::is_pointer<T>::value, std::remove_pointer_t<T>&> dereference(T& t) { 
  return *t; 
}

template<typename T>
std::enable_if_t<!std::is_pointer<T>::value, T&> dereference(T& t) {
  return t;
}

and use it in your function as:

template <class T>
void do_something(T t){
  pass_it_somewhere(dereference(t));
  dereference(t).do_something();
}

Live Demo

This way you'll have to do only with concrete versions of T.

Answer 2

Soultion 1

Use template specialization:

template <class T>
void do_something(T t){
  pass_it_somewhere(t);
  t.do_something();
}

template <class T>
void do_something(T* t){
  pass_it_somewhere(t);    
  t->do_something();
}

Solution 2

Add a user-defined pointer operator in class T:

class A
{
public:
    void do_something() const {}        
    const A* operator->() const { return this; }
};

template <class T>
void do_something(T t){
  pass_it_somewhere(t);      
  t->do_something();
}