Re: avoiding temporaries

From:

"kanze" <kanze@gabi-soft.fr>

Newsgroups:

comp.lang.c++.moderated

Date:

23 Jun 2006 20:59:04 -0400

Message-ID:

<1150970431.472821.259820@i40g2000cwc.googlegroups.com>

Gene Bushuyev wrote:

"Marek Vondrak" <none@none.com> wrote in message
news:e776rl$f7l$1@ns.felk.cvut.cz...

Dear group,

I would like to ask if the following code is legal C++ and
whether NRVO optimization is applicable at operator=().
Consider the following example:

[...]

    Vector operator=( const Vector & v )
        {
        this->~Vector();
        new( this ) Vector( v ); // [1]
        }

This implementation is terrible for so many reasons. Herb
Sutter spent 8 pages explaining why (see Exceptional C++, 41).
Moreover, it won't compile as the function is missing return
statement, and assignment operator normally returns reference,
not copy. So in this case a good solution should be something
like this:

Vector& operator = (Vector v)
{
v.swap(*this);
return *this;
}

Isn't this a bit overkill for his class. A class which consists
of only basic types, and thus cannot possibly throw anything,
ever. In such cases, simply copying does the trick nicely.

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