Re: [boost] [move] problem with msvc and BOOST_MOVABLE_BUT_NOT_COPYABLE

Subject: Re: [boost] [move] problem with msvc and BOOST_MOVABLE_BUT_NOT_COPYABLE
From: David Abrahams (dave_at_[hidden])
Date: 2010-05-28 14:21:38

At Fri, 28 May 2010 19:32:45 +0200,
Thomas Klimpel wrote:
> 
> David Abrahams wrote:
> > > I'm talking about the BOOST_COPYABLE_AND_MOVABLE case. Most compilers
> > > won't do RVO for code written like "X X::create()".
> > 
> > You are claiming that some aspect of that signature causes RVO not to
> > happen?  What aspect?
> 
> I was talking about the signature, but about the way "X X::create()" was written:
> 
> X X::create()
> {
>     X x;
>     return x; // passing value form static memeber-fn
> }
> 

A static member function is just a function to the compiler.  AFAIK,
the only compiler in recent memory that doesn't have NRVO (yet) is
Clang.  And they're working on it.  What compiler are you talking about?

> The expectation that the statement "return x;" will benefit from RVO
> might not be justified here. Writing "return boost::move(x);" might
> actually be a good idea.

There are other scenarios where NRVO won't go into effect and return
boost::move(x) is warranted, 

  X create(bool which)
  {
       X a("foo");
       X b("bar");
       return which ? a : b;
  }

but I don't see anything like that in this case.

-- 
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