传递包装为 unique_ptr C++ 的“this”

Question

I have a class that acts as a node in a binary tree, one of the methods which I would like to call from inside that class is recursive, and needs to pass itself to the next node in the tree so that the next node knows its own parent. I dont want to store a class member parent because I would like to avoid using a shared_ptr.

The code looks something like this:

void MyClass::expand(MyClass* parent){
    for (int i = 0; i < children.size; i ++){
        children[i]->doSomethingWithParent(parent);
        children[i]->expand(this);
    }
    return;
}

But I would like to pass a unique_ptr instead of a raw pointer. However, the pointer to 'this' is already wrapped elsewhere by a unique_ptr already, so I dont want to instantiate another. Is it possible to do this?

If there are any design patterns I should be aware of please let me know.

Any help appreciated

Answer 1

Don't use a pointer at all. You are not taking ownership, the argument is not optional, so use a reference:

void MyClass::expand(MyClass& parent){
    for (int i = 0; i < children.size; i ++){
        children[i]->doSomethingWithParent(parent);
        children[i]->expand(*this);
    }
    return;
}

All of your code will perform the same, and it is safer etc.

Answer 2

If you ever have a situation where you want to pass a non-owning pointer that is guaranteed to be non-null (which appears to be the case here), then you probably want to just use a reference instead.

In your case, depending on what doSomethingWithParent performs, you'd probably actually want a const reference as well:

void MyClass::doSomethingWithParent(const MyClass& parent) {
  // who knows?
}

void MyClass::expand(const MyClass& parent) {
    for (int i = 0; i < children.size; i ++){
        children[i]->doSomethingWithParent(parent);
        children[i]->expand(*this);
    }
}