Re: [boost] [congif] BOOST_BEFRIEND_TEMPLATE, BOOST_PRIVATE

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2005-03-03 19:22:36

----- Mensaje original -----
De: Peter Dimov <pdimov_at_[hidden]>
Fecha: Viernes, Marzo 4, 2005 0:32 am
Asunto: Re: [boost] [congif] BOOST_BEFRIEND_TEMPLATE, BOOST_PRIVATE

> Jonathan Turkanis wrote:
> > Hi,
> > 
> > <boost/shared_ptr.hpp> contains the following in the public section
> > of the class definition (reformatted):
> > 
> >    // Tasteless as this may seem, making all members public
> >    // allows member templates to work in the absence of member
> >    // template friends. (Matthew Langston)
> > 
> >    #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
> > 
> >    private:
> > 
> >        template<class Y> friend class shared_ptr;
> >        template<class Y> friend class weak_ptr;
> > 
> > 
> >    #endif
> > 
> >        T * px;                     // contained pointer
> >        detail::shared_count pn;    // reference counter
> > 
> > This has become a pretty common technique, I believe. I 
> certainly use
> > it a lot, at any rate.
> > 
> > I'd like to suggest two macros which would allow code like the above
> > to be simplified as follows:
> > 
> >    BOOST_PRIVATE:
> >          BOOST_BEFRIEND_TEMPLATE(shared_ptr, Y, 1)
> >          BOOST_BEFRIEND_TEMPLATE(weak_ptr, Y, 1)
> > 
> >          T * px;                     // contained pointer
> >          detail::shared_count pn;    // reference counter
> 
> This doesn't look any better to me than the original, sorry. ;-)

Well, I think there are situations were it'd improve readability:

Example 1: previous section was not public

#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
private:

  template<class Y> friend class shared_ptr;
  template<class Y> friend class weak_ptr;
#else
public:
#endif

Example 2: derivation

class Derived:
#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
private
else
public
#endif
Base
{
...
};

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo