Re: [boost] Re: [any] ostream inserter

From: Sérgio Vale e Pace (svpace.forum_at_[hidden])
Date: 2005-01-28 07:22:27

thank´s

On Thu, 27 Jan 2005 13:47:19 +0000, Tom Widmer <tom_usenet_at_[hidden]> wrote:
> Sérgio Vale e Pace wrote:
> > Tom Widmer wrote:
> >
> >>Anything is convertible to boost::any, and since you have an operator<<
> >>for boost::any, it will catch any object that doesn't have a better
> >>matched operator<< (i.e. any one that doesn't require a user defined
> >>conversion). If this didn't happen, you'd just get a compiler error when
> >>you tried to create an any<A>, since creation of that requires
> >>instantiation of all virtual functions of holder<A>, including the
> >>ill-formed print member (e.g. no overload matches the call out<<held).
> >
> >
> > that explains it, thank's
> >
> >
> >>Dispatching to some kind of default call (which might just set failbit
> >>on the stream, or you could make it configurable) is probably the best
> >>way to handle this.
> >
> >
> > could you elaborate on that, what do you mean by defaul call?
> 
> Every instantiation of holder will have to have a valid, compilable
> print member, since virtual functions are instantiated even if they
> aren't used. So, where a type isn't streamable, you need some kind of
> default behaviour for print just to get the code to compile. I suggested
> setting failbit on the stream, but you may prefer something else, or to
> make it configurable.
> 
> Tom
> 
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