Re: return value optimization

Hi,

I'm designing a Matrix class so I read what Bjarne Stroustrup has on=

section 22.4.6 about it. It shows that it is possible to eliminate t=

temporaries by delaying the construction of the object. In his examp=

(page 675):

struct MVmul {
const Matrix& m;
const Vector& m;

MVmul(const Matrix& mm, const Vector& vv) : (mm), v(vv) { }
operator Vector(); // evaluate and return result
};

inline MVmul operator*(const Matrix& mm, const Vector& vv)
{
return MVmul(mm,vv);
}

Now, I think that's cool, however, I have a question about the
converting function operator Vector(). The implementation could be
done there OR it can be done as a constructor of the Vector class,
right? Something like this:

class Vector {
// member variables
...
public:
// constructors
...
Vector(const MVmul& mvmul) {
// evaluate
}
...
// rest of the class
};

Now the question is, is an approach better than the other? I think
that both are equivalent, but I wanted to make sure asking to the
experts...