Re: [boost] [congif] BOOST_BEFRIEND_TEMPLATE, BOOST_PRIVATE

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2005-03-03 17:21:49

----- Mensaje original -----
De: Jonathan Turkanis <technews_at_[hidden]>
Fecha: Jueves, Marzo 3, 2005 9:49 pm
Asunto: [boost] [congif] BOOST_BEFRIEND_TEMPLATE, BOOST_PRIVATE

> 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.

FWIW, I've also been forced to use a similar workaround.

> 
> 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
> 

BOOST_PRIVATE seems a little to uninformative a name to me.
The macros I'm using are:

BOOST_PRIVATE_IF_MEMBER_TEMPLATE_FRIENDS 
BOOST_PROTECTED_IF_MEMBER_TEMPLATE_FRIENDS 

(well, I'm using lib-specific variations of these names,
but you get the idea.)

As for your proposal, I like it: there are at least three
libraries that would benefit from it.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo