manpreet Best Answer 2 years ago

Background

With normal pointers">pointers, I can do something like the following

void conditional_reassign(MyClass* ptr)
{
    if (my_condition)
    {
        delete ptr;
        ptr = new MyClass(new_param);
    }
}

And I can pass in the pointer I want to change like following

MyClass* ptr = new MyClass(old_param);
conditional_reassign(ptr);

I wish to reimplement this with std::unique_ptr. Here's what I came up with

std::unique_ptr<MyClass> conditional_reassign2(std::unique_ptr<MyClass> ptr)
{
    if (my_condition)
    {
        ptr = std::make_unique<MyClass>(new_param);
    }
    return std::move(ptr);
}

And I would call it with the following

std::unique_ptr<MyClass> ptr = make_unique<MyClass>(old_param);
ptr = std::move(conditional_reassign2(std::move(ptr)));

Question

I'm not quite happy with the verbosity of the line

ptr = std::move(conditional_reassign2(std::move(ptr)));

Is there a way to implement conditional_reassign2 so that I can call it in a manner similar to conditional_reassign(ptr)

manpreet 2 years ago

Either you need to pass the pointer by reference

void conditional_reassign2(std::unique_ptr<MyClass>& ptr) {...}

std::unique_ptr<MyClass> myPtr;
conditional_reassign2(myPtr);

or return the pointer, which requires a single move

std::unique_ptr<MyClass> conditional_reassign2(std::unique_ptr<MyClass> ptr) {...}

std::unique_ptr<MyClass> myPtr;
myPtr = conditional_reassign2(std::move(myPtr));

Also you can return ptr directly from the function without explicitly calling move.

std::unique_ptr<MyClass> conditional_reassign2(std::unique_ptr<MyClass> ptr)
{
    if (my_condition)
        ptr = std::make_unique<MyClass>(new_param);
    return ptr;
}