Single level Inheritance

[awryavari]

Hello All,

I have case where I create one instance of a class "Base" and there are various other child objects that I need to create ("Derived" from "Base"). Is there a pattern where I could ensure that once I create a base class instance in memory, all derived classes refer the same base instance ?

class Base{
//..functions etc
}

class Derived: public Base{

//Needs all functionality of Base...

//Overrides a few methods of Base ..
}

Now i first create a Base* pB = new Base();

I need to create a large number of derived objects and wanted to ensure that everytime I do a Derived* pD = new Derived(); I create the derived object and the base object but the base always refers to the exact same instance of "base" created right at the beginning.

I hope this does not sound confusing. Apologies for the same if it is.

Kindly let me know your comments.

Thanks,
Deepak

[sicarie]

Hello All,

I have case where I create one instance of a class "Base" and there are various other child objects that I need to create ("Derived" from "Base"). Is there a pattern where I could ensure that once I create a base class instance in memory, all derived classes refer the same base instance ?

class Base{
//..functions etc
}

class Derived: public Base{

//Needs all functionality of Base...

//Overrides a few methods of Base ..
}

Now i first create a Base* pB = new Base();

I need to create a large number of derived objects and wanted to ensure that everytime I do a Derived* pD = new Derived(); I create the derived object and the base object but the base always refers to the exact same instance of "base" created right at the beginning.

I hope this does not sound confusing. Apologies for the same if it is.

Kindly let me know your comments.

Thanks,
Deepak

Anyone, please correct me if I am wrong, but as I understood inheritance, there did not need to be an instantiated "base" class - you can directly instantiate a derived class, and that will hold all the same methods (unless overridden) as the base class, as well as default values. Other than that, I believe you need to instantiate all derived classes to have the base values you require.

[Ganon11]

Sicarie is correct. A derived class instance has nothing to do with its base class. For example, consider a very simple class inheritance hierarchy:

Superclass: Mammal (class Mammal)
Subclass: Cat (Cat extends Mammal) (class Cat : public Mammal)
Subclass: Dog (Dog extends Mammal) (class Dog : public Mammal)

Subclass: Chihuahua (Chihuahua extends Dog) (class Chihuahua : public Dog)
Subclass: GermanShepherd (GermanShepherd extends Dog) (class GermanShepherd : public Dog)

Now, if I create a Dog instance, as in Dog myPet = new Dog;, and then want to create a GermanShepherd instance (GermanShepherd myPuppy = new GermanShepherd;), does myPuppy have anything to do with myPet? No! myPuppy is-a Dog, so it has a relationship to the class Dog, but not to any particular instance of Dog.

Any GermanShepherd I create has nothing to do with any Dog I create - but every GermanShepherd and Chihuahua I create is-a Dog. This is the only relationship involved in inheritance.