So I have a generic "game" system. The base "game" is abstract, and there's 
a bunch of "screen" classes you can stack up (like "main menu" is under 
"start menu" is under "select players popup" and etc.)

Now, a bunch of the abstract screens (like "pause menu" and "join network 
game menu") are all supposed to have the same "background" behind them. The 
framework I'm looking at has all the classes that are that sort of menu 
(i.e., that want to show a generic background (like a scrolling starfield, 
or some scene from the game, or etc)) inherit from "backgroundscreen", which 
you copy and replace for yourself. I.e., all these are cut-and-paste 
programming.

I'd prefer to have a "please log in" screen that's going to be the same menu 
and behavior but different background all be concrete, inheriting from an 
abstract class you replace for each game.

So, basically, I want a bunch of concrete library classes (A), all 
inheriting from the same game-specific class (B), which in turn inherits 
from an abstract library class (C).

I'm pretty sure even multiple inheritance would be unhappy with that.

Something like Python or Ruby could monkey-patch the inheritance tree at 
run-time, but that's awful.

Right now, I have three solutions. Each (A) class inherits from a concrete 
version of (C), which calls a game-specific factory-like method with the 
type of (A) as a parameter to draw the background.

Alternately, each (A) actually stacks a (B) underneath in the screen stack, 
and I fix the manager of the screen stack to draw the screens underneath 
first, and then make sure the (A) classes don't clobber the background 
already drawn.

Alternatively, I make the "draw a background" a completely separate 
component that gets turned on or off depending on whether the code wants the 
background, or depending on the top-most screen of the screen stack. This is 
kind of what I'm leaning towards.

But I thought it was an interesting question in OO Design.

-- 
Darren New, San Diego CA, USA (PST)
   Linux: Now bringing the quality and usability of
   open source desktop apps to your personal electronics.

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