What is the purpose of pure virtual destructor? [duplicate]

Question

Possible Duplicates:
Under what circumstances is it advantageous to give an implementation of a pure virtual function?
Why do we need a pure virtual destructor in C++?

Compiler doesn't force the Child class to implement a destructor when its Base has pure virtual destructor.

struct Base
{
  virtual void foo () = 0;
  virtual ~Base() = 0;
};
Base::~Base() {} // necessary

struct Child : Base
{
  void foo() {}
  //ok! no destructor needed to create objects of 'Child'
};

Funny part is that; compiler rather forces the Base to define a destructor body. Which is understood. (Demo for reference)

Then what is the purpose of having pure virtual destructor in Base class ? (Is it just to disallow Base creating objects?)

Answer 1

Sometimes an abstract base class has no virtual methods (= often called a “mixin”) or no methods at all (= often called a “type tag”).

To force those classes to be used as abstract base classes, at least one method needs to be pure virtual – but the classes don’t have virtual methods! So we make the destructor pure virtual instead.

Answer 2

It makes the class abstract. The existance of at least a pure virtual method is sufficient for a class to be abstract.