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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


    Self& operator=(Self rhs) { swap(rhs); return *this; } // strong

I was able to find a post by Valentin Bonnard also suggesting the same:


"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.

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