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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.

Dave Abrahams           Meet me at BoostCon:
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