Cumulative

[qznc]

On Monday, 24 February 2014 at 08:41:06 UTC, Steve Teale wrote:
> 25 years ago, when I was trying to write some sort of library 
> to go with Walter's C++ compiler, I had a wish, and it still 
> pops into my head from time to time.
>
> What I wanted was functions that were declared in a base class 
> as 'cumulative', or something similar. They would have been 
> generally like virtual functions, except that any derived class 
> that wanted to do something extra - as opposed to something 
> different, would simply define an 'extend', and just specify 
> the extra code. The compiler would then automatically add a 
> call to the same function in whatever base class last defined 
> or extended the method.
>
> extend void foo()   // Declared in base class as cumulative 
> void foo()
> {
>    (cast(BaseClass) this).foo();  // Compiler does this for you
>                                   // similar to changing a 
> light bulb ;=)
>
>    // the extra stuff
> }
>
> I think also that it might be necessary for the base class 
> function to return on behalf of the derived method as opposed 
> to to it.
>
> Does this make any sense?
>
> Steve

Sounds a little like the :after mechanism of the Common Lisp 
Object System (CLOS). They also have :before, if your extra code 
should run before the super-call. The third variant is :around, 
which is like the default overwriting in D et. al.