Re: [boost] [xint] Third release is ready, requesting preliminary review

Subject: Re: [boost] [xint] Third release is ready, requesting preliminary review
From: DE (satan66613_at_[hidden])
Date: 2010-05-04 11:56:29

on 04.05.2010 at 19:36
 Giovanni Piero Deretta wrote :
> Then you haven't read the article carefully enough ;)

> The idea is that rvalues passed to operator- (like in Peter's example)
> won't be copied due to elision of temporaries. Only lvalue parameters
> will be copied (you can't avoid that of course), while in your example
> you have an unconditional copy to initialize ret.

oh! now i get it
the argument _must_ be passed by value for copy elision to be possible
is that right?

>> what about idiomatic
>>
>>  return X().swap(x);  //x is modified

> my swap functions (and IIRC standard container swap functions) usually
> return void so it won't work in generic code, but if it works for your
> case, sure. Usually I refactor the pattern in a function like this:

> template<typename T>
> T move_swap(T& x) { // T is default constructible and swappable
>    T ret;
>    using std::swap;
>    swap(x, ret);
>    return ret;
> }

> So your operator- would look like this:

> X operator- (X x)
> {
>    modify x;
>    return move_swap(x);
> }

you are absolutly right about swap()
but that move_swap seems a truly perversion to me now

...
however now i can find some logic under it

-- 
Pavel
P.S.
if you notice a grammar mistake or weird phrasing in my message
please point it out