Question

I am having my first attempt at using C++11 unique_ptr; I am replacing a polymorphic raw pointer inside a project of mine, which is owned by one class, but passed around quite frequently.

I used to have functions like:

bool func(BaseClass* ptr, int other_arg) {
  bool val;
  // plain ordinary function that does something...
  return val;
}

But I soon realized that I wouldn’t be able to switch to:

bool func(std::unique_ptr<BaseClass> ptr, int other_arg);

Because the caller would have to handle the pointer ownership to the function, what I don’t want to. So, what is the best solution to my problem?

I though of passing the pointer as reference, like this:

bool func(const std::unique_ptr<BaseClass>& ptr, int other_arg);

But I feel very uncomfortable in doing so, firstly because it seems non instinctive to pass something already typed as _ptr as reference, what would be a reference of a reference. Secondly because the function signature gets even bigger. Thirdly, because in the generated code, it would be necessary two consecutive pointer indirections to reach my variable.

Answer 1

If you want the function to use the pointee, pass a reference to it. There’s no reason to tie the function to work only with some kind of smart pointer:

bool func(BaseClass& base, int other_arg);

And at the call site use operator*:

func(*some_unique_ptr, 42);

Alternatively, if the base argument is allowed to be null, keep the signature as is, and use the get() member function:

bool func(BaseClass* base, int other_arg);
func(some_unique_ptr.get(), 42);