Re: [boost] Re: Formal Review Request: iostate.zip

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-02-03 11:03:03

----- Original Message -----
From: "Daryle Walker" <darylew_at_[hidden]>

> I tried something like
>
> template < class ObjectType, typename AspectType, AspectType
(ObjectType::*
> Getter)(), AspectType (ObjectType::* GetSetter)(AspectType) >
> class get_set_base
> {
> public:
>     explicit get_set_base( ObjectType &o )
>               : s_( &o ), a_( o.*Getter() )
>               {}
>              get_set_base( ObjectType &o, AspectType a )
>               : s_( &o ), a_( o.*GetSetter(a) )
>               {}
>             ~get_set_base()
>               { s_->*GetSetter(a_); }
>
> private:
>     ObjectType * const  s_;
>     AspectType const    a_;
> };
>
> But my compiler choked on the third template parameter, saying it was an
> unimplemented feature.

That'll choke MSVC as well, at least in some circumstances. However, you can
use intermediary policies to get around this problem:

template < class ObjectType, typename AspectType, class Accessor >
class get_set_base
{
public:
    explicit get_set_base( ObjectType &o )
              : s_( &o ), a_( Accessor::get(o) )
              {}
             get_set_base( ObjectType &o, AspectType a )
              : s_( &o ), a_( Accessor::get_set(o, a) )
              {}
            ~get_set_base()
              { Accessor::get_set(*s_, a_); }

private:
    ObjectType * const  s_;
    AspectType const    a_;
};

Accessor is a policies class which supplies get/get_set as static member
functions.