🚀 go-pugleaf

James Christodouleas (jchristo@mit.edu) wrote:
: In article <4jdvnj$o35@mulga.cs.mu.OZ.AU>, fjh@munta.cs.mu.OZ.AU (Fergus
: Henderson) wrote:

: > Philippe Verdy <100105.3120@compuserve.com> writes:
: > 
: > >template <class T, class CT>
: > >class SmartPtr2  {
: > >   SmartPtr2(T* p) { mp = const_cast<CT>(p) ; }
: > >   CT & Dereference() {
: > >     return *mp ;
: > >   }
: > > private :
: > >   CT *mp ;
: > >} ;
: > >template <class T> class ConstSmartPtr : SmartPtr<T, T> {} ;
: > >template <class T> class FreeSmartPtr : SmartPtr<T, const T> {} ;
: > 
: > You forgot to delegate the constructors.
: > 
: > (Of course, if C++ supported tempate typedefs, there wouldn't be
: > any need to delegate constructors in examples like this.
: > Unfortunately it doesn't.)

: What does it mean to "delegate constructors?"  I looked it up in Coplien,
: Advanced C++, and he talks about delegation to mean different classes
: sharing functionality dynamically.  

He means that the new classes, ConstSmartPtr and FreeSmartPtr do not
have constructors, and cannot be created, so constructors that
simply pass on the parameters are required (delegation).

There's another problem anyway - Phillippe used private inheritence,
so a user cannot access the Dereference member function anyway.

	[Moderator's note: and `SmartPtr' should be `SmartPtr2',
	 and `const_cast<CT>' should be `const_cast<CT*>'.  This is
	 why it is a good idea to try compiling your examples
	 before posting them ;-).  -fjh. ]

-- 
        Tony Cook - tony@online.tmx.com.au
                    100237.3425@compuserve.com
---
[ comp.std.c++ is moderated.  To submit articles: try just posting with      ]
[ your news-reader.  If that fails, use mailto:std-c++@ncar.ucar.edu         ]
[ FAQ:      http://reality.sgi.com/employees/austern_mti/std-c++/faq.html    ]
[ Policy:   http://reality.sgi.com/employees/austern_mti/std-c++/policy.html ]
[ Comments? mailto:std-c++-request@ncar.ucar.edu                             ]