Re: C++11 rvalue reference question

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From	Dave Abrahams <dave@boostpro.com>
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Subject	Re: C++11 rvalue reference question
Date	Tue, 6 Dec 2011 11:59:50 -0800 (PST)
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Cross-posted to 2 groups.

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on Mon Dec 05 2011, Andrew Tomazos <andrew-AT-tomazos.com> wrote:

> In C++03 many times it was recommend to write such a function as
> follows:
>
> void f(O& out, const I& i)
> {
>     .... // mutate result based on i
>     if (,,,)
>        throw E(...);
> }
>
> I i = ...;
> O o;
> f(o,i);
>
> I suspect this is to avoid the (potentially expensive) copy
> construction as the temporary O instance is copied from f's stack
> frame to the callers.

Probably, but the code above has always been a bad idea even in C++03.
Every compiler implements copy elision, so

  O o = f(i);

is bound to be just as efficient, if not more so.

http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/

Cheers,

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com


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Thread

C++11 rvalue reference question Andrew Tomazos <andrew@tomazos.com> - 2011-12-04 21:38 -0800
  Re: C++11 rvalue reference question Daniel Krügler <daniel.kruegler@googlemail.com> - 2011-12-05 15:44 -0800
  Re: C++11 rvalue reference question Arne L <a.luenser@googlemail.com> - 2011-12-05 15:51 -0800
    Re: C++11 rvalue reference question SG <s.gesemann@gmail.com> - 2011-12-06 12:00 -0800
  Re: C++11 rvalue reference question Dave Abrahams <dave@boostpro.com> - 2011-12-06 11:59 -0800
    Re: C++11 rvalue reference question Ebenezer <woodbrian77@gmail.com> - 2011-12-11 00:52 -0800

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