Subject: Re: [boost] Improving the assignment operators of various Boosttypes
From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-09-10 07:41:09
Niels Dekker:
>>> T& operator=(T arg)
>>> {
>>> arg.swap(*this);
>>> return *this;
>>> }
...
> Is the choice between swap(arg) and arg.swap(*this)) just a matter of
> taste?
Yes, I think so. I was just saying that
T& operator=( T arg )
{
swap( arg );
return *this;
}
is the form I've seen used (by Dave Abrahams, I think*). It certainly looks
more "idiomatic" (in the sense of being recognizable as an idiom as opposed
to ordinary code) because of the unusual swap call.
*) Turns out that I was right in thinking that. Dave's associative_vector
submission:
http://listarchives.boost.org/Archives/boost/2000/05/3200.php
contains:
Self& operator=(Self rhs) { swap(rhs); return *this; } // strong
guarantee
I was able to find a post by Valentin Bonnard also suggesting the same:
http://tech.groups.yahoo.com/group/boost/message/5001
Incidentally:
http://aspn.activestate.com/ASPN/Mail/Message/boost/1140338
"It doesn't compile with Borland C++Builder 4 or BCC 5.5.
...
The next problem was associative_vector's assignment operator.
Borland didn't recognise it as one and generated a default.
Then it couldn't disambiguate the generated assignment operator
and the one supplied. I changed this to
Self& operator=(const Self &rhs)
{ Self temp(rhs); swap(temp); return *this; }"
My memory is correct on this one, too. I'm not sure why BCC 5.5.1 didn't
exhibit the problem in my tests.