using names before they're defined

[jordan.nick at gmail.com]

Steve Holden wrote:
> 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].

Unfortunately, if he wanted to make the topology more complicated, for
instance having two components downstream, it would be much more
cumbersome to inherit the list object and implement this.

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

That sounds a little arrogant. sorry!

> regards
>   Steve
> --
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