[boost] Object Factory

From: Christophe Meessen (christophe_at_[hidden])
Date: 2002-11-19 13:04:29

Hello

I recently met the need for an Object Factory. I according to some 
configuration information I would instantiate different type of objects 
derived from a same base class.
So I wrote a small and light STL class that would do just what I 
wanted.It might be that such functionality could be usefull for other 
people. I don't know if there is a standrad submission procedure or if 
this is the way to suggest an idea or a draft implementation.

Here is the general usage principle.

In one .cxx file you instantiate the baseFactory singleton object. It is 
accessed through static member variables so does not need to be declared 
as extern.

// Declare the factory
Factory<MyBaseType> baseTypeFactory;

// Declare an instantiable class as global variable
Factory<MyBaseType>::Class<MyDerivedClass1> derivedClass1( 
"DerivedClassOne" );

// Declare another instantiable class as global variable
// In any .cxx file of the file one can declare a new dervied class 
instantiable by the factory.
Factory<MyBaseType>::Class<MyDerivedClass2> derivedClass1( 
"DerivedClassTwo" );

int main()
{
      ...
     // Building objects
     MyBaseType * obj  = 
 Factory<MyBaseType>::buildObject("DerivedClassTwo");
    ...
}
The default class key type is a string. But it may be changed into an 
integer or anything else. The returned value is NULL if the key type 
does not match any know class factory.
In the use case I had, the constructor needed an argument. So my version 
adds an argument to the buildObject method that will be passed to the 
constructor of the object called with new. To follow the STL standard 
one should also be able to add a specific allocator type.

I am not a template expert. So the current implementation may not be the 
one the might please everybody.

Would there be any interrest in such thing for boost ? If there are 
better solution I would be happy to know about it. 

-- 
cheers,
Ch. Meessen