Re: [boost] [operators] The Dangling Reference Polarization

Subject: Re: [boost] [operators] The Dangling Reference Polarization
From: Daniel Frey (d.frey_at_[hidden])
Date: 2013-05-05 04:01:20

On 05.05.2013, at 01:22, Michael Marcin <mike.marcin_at_[hidden]> wrote:

> MSVC11 does do copy elision when only trivial types are involved it seems. For example try instead of std::vector try:
> typedef std::array<std::pair<int,int>,4> pod;
> 
> Direct initialization from rvalue, constructed with pod
> X a(( rvalue(pod()) ))
> ===========
> X5: construct (with pod)
> X5: destroy
> -----------
> 0/1 possible copies made
> 0/1 possible moves made
> 1/1 possible elisions performed

I am not concerned about direct initialization, the important case (for the discussion of Boost.Operators' future) is the "identity( rvalue() )"-case. Of course MSVC (like other compilers) does perform copy elision in some cases, but I am still looking for a case like identity(), where a parameter is pass-by-value and that parameter is returned from the function. Is there some way that the copy/move of the parameter can be avoided? In the test-program I wrote, is there a way to beat STANDARD with PASS_BY_VALUE?