Separating copy/move assignment operator

Question

I've read here: What are move semantics?, under secondary title: Special member functions, the reasons why we should unify both copy assignment operator & move assignment operator into a single move\copy assignment operator,

but what if we wish to forbid copying or moving? should in this case I indicate "deleted" on the forbidden constructor and implement the other? (i.e. separating between the two).

If so, what is the proper way to do it?

Just separate them, like the first two code block in that section — Danh, Dec 05 '16 at 06:46
are you referring to `copy-and-swap` idiom for the assignment operators? — kmdreko, Dec 05 '16 at 06:49
Well, what operations do you want your class to support? It is up to you. — juanchopanza, Dec 05 '16 at 06:58
Also, the "unification" shown has trade-offs. Personally I don't think it is such a good idea. — juanchopanza, Dec 05 '16 at 06:59
I want to forbid copying, but allow moving. To my understanding, the move/copy assignment operators both uses the copy constructor which is forbidden in my case, or if I'm wrong, how should I implement a move assignment operator which doesn't use the copy constructor? — Etay, Dec 05 '16 at 07:04
you create the normal move assignment operator: `X& X::operator=(X&&);` — kmdreko, Dec 05 '16 at 07:09

Miles Budnek · Accepted Answer · 2016-12-05T07:14:33.400

If you want to create a class that is movable but not copyable, you should implement the move constructor and mark the copy constructor as deleted.

The copy-and-swap pattern still works (more of a move-and-swap, really). Since the parameter can only be move constructed, only move assignment will be available.

class MyClass
{
    MyClass(MyClass&& other) {
        // Do your move here
    }
    MyClass(const MyClass& other) = delete;

    MyClass& operator=(MyClass other) {
        // You can still use copy-and-swap (move-and-swap, really)
        // Since MyClass is non-copyable, only move assignment will be available
    }
};

Or you could just create a move assignment operator (MyClass& operator=(MyClass&& other)) instead. The default copy assignment operator will be implicitly deleted if you declare a move constructor.

Thanks a lot! Understood completely. – Etay Dec 05 '16 at 07:16 — Etay, Dec 05 '16 at 07:16

Separating copy/move assignment operator

1 Answers1