Re: Proper way to put an abstract base class into a container

From: Aguilar, James (jfa1_at_cec.NOBOTSwustl.edu)
Date: 08/11/04 

Date: Tue, 10 Aug 2004 22:48:35 -0400

"David Hilsee" <davidhilseenews@yahoo.com> wrote in message
news:jPKdncoEMqCE5YTcRVn-tA@comcast.com...
>
> When people say that they have a class that represents a matrix, they are
> usually writing a class that will perform number-crunching (matrix
> multiplications, inverses, transposes, etc).

This is not a mathematical matrix, it is a matrix in the sense of a two
dimensional array (i.e. rows and columns, hence, matrix).

> Also, they usually will use it
> to hold objects of type double or float (or possibly a light wrapper
around
> those types), and not instances of an ABC. An ABC might be an interesting
> exercise, but for any application that made intensive use of the matrix,
the
> performance would probably be unacceptable.

I wouldn't say that. It's just a one dimensional array of "<typename T>"s.
It is accessed through T operator ()(int, int) which just does array
arithmetic: return store_[rows * x + y]. Everything is inline, so it's
really no overhead at all, besides actually filling the matrix.

> Why do you want to store an ABC
> inside a matrix?

I'm doing a toy project which makes a 80x20 matrix of containers, then puts
particles in them (based on a text file). After that, it will iterate
through the matrix and randomly move each particle. The point is to
demonstrate that a gas, even if concentrated in one place initially, will
eventually diffuse into a larger area. This will be tried with all kinds of
shapes of containers to see how well the concept works and what kinds of
shapes keep gasses in the longest. Since a text file will dictate the shape
of the container, it should be no problem to reuse the programs on different
kinds of containers. Of course, the base class that I want to put into the
matrix is the bottom type (that is "Floor" or "Wall" at this point) which
will itself have a reference to a list of the particles on top of it.

> As Victor pointed out, pointers are an option. They're
> not all that easy to handle, though, if you want to write memory-leak-free
> code.

That's one option. I'm not worried about memory leaks, since the program is
so small. I know exactly where everything is and in what order it happens.
Pointers . . . meh. I guess I will have to use one sometime, so it might as
well be now. I think I'll do that. Actually, I think I can still abstract
it and make it return references to the typename by making pointers
internally but dereferencing them outside. Well, I'll let y'all know how it
goes.

Yours,

James

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