Re: rvalue references and parameter passing
Am Mittwoch, 3. Oktober 2012 01:23:30 UTC+2 schrieb fmatthew5876:
Suppose I have this:
class Matrix4 {
public:
//stuff
private:
float _m[16];
};
Matrix4 operator+(Matrix4 l, const Matrix4& r) {
l += r;
return l;
}
Is there any possible scenario where I would want to also create
a version of operator+ that uses rvalue references? i.e.
Matrix4 operator+(Matrix4 l, const Matrix4&& r) {
l+=r;
return l;
}
No, not really -- not with this class.
I understand rvalue references are desirable in most cases because we
want to use move constructors instead of making unnecessary copies.
But in this particular case, the matrix class directly contains its
data instead of doing an allocation so there is no move constructor.
Right.
To put it more succinctly, is there ever a case when the first operator+
will create a copy for the second argument where the second operator+
would not?
No. None that I can think of. Rvalue references don't magically avoid
copies. They are just means to hold on to "temporary" objects with write
access to them. The magic of movable types happens in their respective
move operations (ctor, assignment, etc).
Cheers!
SG
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