Re: Defininng and using an object as a Swarm and a SwarmObject at the same time.

[Alex Lancaster]

>>>>> "JV" == Joseph E Villa <address@hidden> writes:

JV> It seems what you've proposed is multiple inheritance. There's
JV> certainly a lot of discussion in OO design about multiple
JV> inheritance, and some would have you believe it is inheritantly
JV> (*g*) problematic from a pure design perspective. (I tend to stay
JV> away from multile inheritance, but I suspect this is one of those
JV> religious fervor topics.)

JV> You may be able to achieve multiple inheritence by including the
JV> SwarmObject.h and Swarm.h files in your Population
JV> files. (Cruising through some of the root Swarm classes, I think I
JV> came across this.)

Unfortunately this won't work (we don't use multiple inheritance
anywhere in the Swarm kernel).  Objective C (and therefore Swarm)
doesn't support multiple-inheritance directly (C++ does, but Java
doesn't).  But there are several ways to achieve a similar effect.
You can use Objective C protocols (to construct classes that conform
to a given interface, but that doesn't necessarily allow you access to
the *implementation*, like true multiple inheritance does).

Here's an online reference from the NeXT Objective C manual (now
hosted on the Apple website):

  
http://developer.apple.com/techpubs/macosxserver/System/Documentation/Developer/YellowBox/TasksAndConcepts/ObjectiveC/moreobjc.htm#787

The other approach is to use forwarding to mimic multiple inheritance,
the NeXT book on Objective C discusses this approach in more detail:

  
http://developer.apple.com/techpubs/macosxserver/System/Documentation/Developer/YellowBox/TasksAndConcepts/ObjectiveC/runtime.htm#1005

The top level for this online Objective C book is at:

  http://developer.apple.com/techpubs/macosxserver/ObjectiveC/index.html


 -- Alex

-- 
  Alex Lancaster           |  e-mail: address@hidden
  Swarm Program            |     web: http://www.santafe.edu/~alex
  Santa Fe Institute       |     tel: +1-(505) 984-8800
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