Re: [boost] [intrusive] rtti_base class proposition

Subject: Re: [boost] [intrusive] rtti_base class proposition
From: Ireneusz Szpilewski (irek_at_[hidden])
Date: 2009-10-20 13:47:38

Stewart, Robert wrote:Stewart, Robert wrote:
 > Ireneusz Szpilewski wrote:
 >  
 >> class rtti_base
 >> {
 >>      virtual void _dummy() {}
 >> };
 >>    
 >
 > Once you have virtual functions, you need a virtual destructor.  
Hence the base class should define a virtual destructor and then there's 
no need for _dummy().
 >
 >  
Great idea! :-D
 >> Every class deriving from rtti_base can be queried
 >> by means of RTTI, in particular rtti_base class
 >> and dynamic_cast can be used in similar way
 >> as IUnknown and QueryInterface() in
 >> COM Object Model
 >>    
 > [snip]
 >  
 >> The main purpose of this class is
 >> to set some standard name for that
 >> pointer type.
 >>    
 >
 > Why is a common, standardized or de facto standard name needed?  The 
usual case is to create a base class for each context in which a common 
base is desired.
 >  
Because that could be a C++ standard common class as Object in C# or
IUnknown in COM.
Let's call it object_t. ;-)
Just not forced by language rules, but used at will if needed.
Anyone could attach to it and have generic pointer to objects.

As in my example above, I  have a room  where  are  cats and girls.
I want  to give  milk to  cats and  kiss  girls.

There are two classes:

class Cat
{
  public:
   void GiveMilk();
};

class Girl
{
  public:
  void Kiss();
};

they have really nothing in common, but objects of both classes are in 
my room.
So I add to them something by which I can hold them all via pointers,
and, in addition, query about their types.

Let's suppose you have the same problem with different (or not) classes
and have used also rtti_base to hold them all.
Then we both win! You can insert your objects into  my container,
and  if  by accidence they derive from Cat or/and Girl, they will be
pleased in my  room.  If  I  put  my  objects  into  your  collection
std::stack<rtti_base*> for example, they  can  also  be  pleased  if
you GiveMilk() to Cats and Kiss() Girls. :-)

(By the way std::shared_ptr<rti_base*> would give us
C++ equivalent of IUnknown interface with metods:
QueryInterface();
AddRef();
Release();
)

Ireneusz  Szpilewski