Re: [boost] boost::mem_fn suggestion/question

From: Piyo (cybermax_69_at_[hidden])
Date: 2007-05-15 14:31:46

Peter Dimov wrote:
> 
> I'm somewhat reluctant to introduce features into boost::mem_fn since 
> std::tr1::mem_fn and the upcoming std::mem_fn don't/won't have them. If you 
> start using ::argN_type, you won't be able to switch to std::mem_fn once it 
> becomes available. Of course if this is not a concern for the Boost 
> community we can easily add the typedefs and the arity. 
> 

Hi Peter,

Several questions:
- when C++0x gets published and when compilers are fully tr1 compliant,
do you see boost::mem_fn (and the rest of the tr1 overlap) go away from
boost?
- I was also interested into the rationale why it was omitted also.
I was looking at the mem_fn tr1 proposal and noticed that argN_types
were not mentioned. Was it simply because no one so far wanted it?

Also, just to complement Marcus's use case, here is a real-world
(simplified) use-case that my co-worker is encountering.
----------------------------------------------------------------------
template <typename BaseClassType>
class ClassPool
{
public :
     void addClass(const std::string &key, BaseClassType *instance)
     {
         m_objectMap[key] = instance;
     }
     template <typename MemFnType>
     void executeMemberFunction(const std::string &key, MemFnType memFn)
     {
         //here is where we need the class type of the member fn
         typedef MemFnType::ClassType DerivedType;
         //we need to dynamic cast to the derived type so we can call
         //the member function on it
         typename DerivedType *derivedObject =
             dynamic_cast< DerivedType *>(m_objectMap[key]);
         //call the member function
         memFn(derivedObject);
     }
     std::map<std::string, BaseClassType *> m_objectMap;
};
class BaseClass
{
};
class DerivedClass : public BaseClass
{
     void someFunction() {};
};
void main()
{
     ClassPool<BaseClass> classPool;
     classPool.addClass("SomeObject",new DerivedClass);
 
classPool.executeMemberFunction("SomeObject",boost::mem_fn(someFunction));
}