RFC: New C++ Attribute: final

[Kevin Atkinson <kevina at gnu dot org>]

I have an idea for a new C++ attribute, and would like to know what others 
think of it:

'final'

Marks a virtual function of an entire class as being "final", in the sense 
that it can not be overridden in a derived class.  If it is applied to a 
type then every virtual function in the class will be considered final.  
It will not, however, keep a class from being inherited from.  
Gcc will produce a warning (or maybe an error) if a "final" method is 
overridden.

The primary purpose of this attribute is to serve as an optimization hint 
so that a virtual function call does not need to be used.  It will also 
allow gcc to perhaps inline the function call if it is appropriate.

An example:

class A {
public:
  virtual void f();
};

class B {
public:
  __attribute__((final)) void f();
};

int main()
{
  B * b = new B;
  A * a = b;
  a->f(); // virtual call
  b->f(); // non virtual call since the function in type B is marked
          // as final
  b->B::f(); // equalvent to the above
}

I have not written any code for GCC yet, but if people think it is a good 
idea I may just implement this, as it seams like something that can't be 
too difficult to do.

-- 
http://kevin.atkinson.dhs.org