using names before they're defined

[Steve Holden]

davehowey at f2s.com wrote:
> I have a problem. I'm writing a simulation program with a number of
> mechanical components represented as objects. When I create instances
> of objects, I need to reference (link) each object to the objects
> upstream and downstream of it, i.e.
> 
> supply = supply()
> compressor = compressor(downstream=combustor, upstream=supply)
> combuster = combuster(downstream=turbine, upstream=compressor)
> etc.
> 
> the problem with this is that I reference 'combustor' before is it
> created. If I swap the 2nd and 3rd lines I get the same problem
> (compressor is referenced before creation).
> 
> 
> aargh!!! any ideas on getting around this?
> 
Yes. You are building a generic data structure, so you shouldn't really 
be trying to store individual objects in variables like that. You need a 
data structure that's appropriate to your problem.

For example, you could consider storing them in a list, so you have

components = [supply(), compressor(), combuster()]

Then components[n] is upstream of components[n-1] and downstream of 
components[n+1].

In short, your thinking about data representation might need to become a 
little more sophisticated.

regards
  Steve
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