CODEWITHSUNDEEP
c++
johnbakers
johnbakers

Reputation: 24771

Does this assignment create a copy?

Will creating this new object, v, result in an entirely new object or simply the same object space referenced by *this?

Vector2 v = *this;

I would not expect it is actually creating a new object, but I'm seeing this code in a sample app that then manipulates this new object even though this code is in a class function that is set as const. Thus I would expect that this object,v, is in fact entirely a separate memory space than *this.

Upvotes: 2

Views: 101

Answers (3)

Gorpik
Gorpik

Reputation: 11038

Assuming that you are inside a Vector2 method, this operator = you are using is called copy assignment for a reason. Now, whether it does a deep copy, a shallow copy (copies pointers, but not the objects pointed by them) or whatever is down to the actual implementation of the operator.

Upvotes: 1

NPE
NPE

Reputation: 500673

Yes, v is an entirely new object to *this.

Upvotes: 0

Luchian Grigore
Luchian Grigore

Reputation: 258618

It's creating a new object, yes - but by initialization, not assignment.

You can however bypass that by using references, Vector2& v = *this;, in which case v is an alias for *this (or const Vector& v = *this, if the method is const).

The reasons for this is exactly the one you stated - since the method in which this happens is const, there's no way to mutate *this - so you need a non-const copy of it.

Upvotes: 5

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