Re: [boost] Re: Re: Re: New patch for operators.hpp uploaded

From: David Abrahams (dave_at_[hidden])
Date: 2002-10-22 17:23:59

Daniel Frey <d.frey_at_[hidden]> writes:

> On Tue, 22 Oct 2002 22:14:26 +0200, David Abrahams wrote:
> 
> > Daniel Frey <d.frey_at_[hidden]> writes:
> > 
> >> this is equivalent to:
> >> 
> >> T operator+( const T& lhs, const T& rhs ) {
> >>    return T( lhs ).operator+=( rhs );
> >> }
> > 
> > Not neccessarily. It's possible to implement += as a free function. I'm
> > not sure if that's relevant to your argument or just a red herring.
> 
> Well, OK, it could be a free function, but
> 
>    return operator+=( T( lhs ), rhs );
> 
> doesn't look any better wrt RVO, does it? ;)

My attention is divided at the moment, so I can't answer with
authority. I trust your analysis.

> > I don't know how well that works. You need to know that T
> > implements the appropriate constructor, which AFAICT isn't
> > possible for a generic function.
> 
> Are you talking about a Mojo-friendly implementation? 

Yeah.

> > I offered to run any test program posted, but nobody gave me one to try.
> 
> Oh, I think I can change that:
> 
> #include <iostream>
> using namespace std;
> 
> struct X
> {
>    X() { cout << "X"; }
>    X( const X& ) { cout << "C"; }
> };
> 
> X f()
> {
>    return X();
> }
> 
> X g()
> {
>    X x;
>    return x;
> }
> 
> int main()
> {
>    X x1( f() ); cout << endl;
>    X x2( g() ); cout << endl;
> }

gcc-2.95.3
X
XC

gcc-3.0.4
XC
XCC

gcc-3.2:
X
X

cwpro7.2:
XC
XCC

cwpro8.2
X
XC

cwpro8.3:
X
X

vc6:
X
XC

vc7:
X
XC

vc7.1:
X
XC

intel C++ 5.0
XC
XC

intel-6.0
XC
XC

intel 7 beta (no optimization - release mode fails to link):
XC
XC

-- 
                    David Abrahams
dave_at_[hidden] * http://www.boost-consulting.com
Building C/C++ Extensions for Python: Dec 9-11, Austin, TX
http://www.enthought.com/training/building_extensions.html