[boost] Re: Herb Sutter's Assignment operator can be optimized + Proposal for very small boost utility library

4 Mar 2005

      Pavel Chikulaev writes:
...
Do you know that well-known Herb Sutter's assignment operator in most cases 
does unnecessary copying? No? Then read it to learn how to elminate it.
[...]
...
But how can we define that copying is necessary? - Every function returns 
object not of type T but temporary object of type T. So let's code 
something:
template<typename T>
struct temporary : T
{
    temporary() {}
    temporary(const T & t) : T(t) {}
//some operators and constructors to create base object in-place not 
listed here
};
Now let's change function consider operator +:
Matrix operator + (const Matrix & a, const Matrix & b)
{
    Matrix temp(a);
    temp += b;
    return temp;
}
To optimize it we do the following:
temporary<Matrix> operator + (const Matrix & a, const Matrix & b)
{
    Matrix temp(a);
    temp += b;
    return temp;
}
[...]

That's called "move semantics", a library-based approach to which was
thought of as far back as 2001 -- http://tinyurl.com/4nzcq
(http://groups-beta.google.com/group/comp.lang.c++.moderated/browse_thread/th...).

-- 
Aleksey Gurtovoy
MetaCommunications Engineering