TITLE: Pure virtual methods may have implementations 


This information was take from the ARM (Annotated C++ Reference
Manual), page 214-216.


Pure virtual methods are allowed to have an implementation (contrary
to popular belief). For example,


class A {
	virtual void f () = 0;
};

void A :: f () {
	...
}


Note that the method f may be called explicitly because this bypasses
the virtual mechanism. We try the following as constructors:


A() 
{ 
	f();     // illegal, results undefined
}

A() 
{ 
	A::f();  // legal
}


[There is some debate about what constitues appropriate use of
a pure virtual function with implementation, but it is an
argument of convention.]