naming convention based file toggling facility

[Robert Anderson <rwa@alumni.princeton.edu>]

I've had a hackish little elisp function for years that always struck me
as a slightly surprising omission from emacs: the ability to toggle
between files based on a naming convention like: <source>.c and
<source>.h.

This of course, generalizes to more contexts.  I use it for toggling
between header, implementation, and unittest files, for example, based
on the convention that the corresonding unittest file is
<source>-test.c.  I'm sure it's useful elsewhere, given a reasonable
method for defining the relationship between the names of the related
files.

This kind of "toggle header" or "toggle source" function is standard IDE
fare.  I got used to it from a previous life when I was using Metrowerks
Codewarrior.  It's _very_ handy, IMO.

Is there some reason that such a thing is not included in emacs?  Maybe
it's there and I've missed it?  Would the maintainers be interested in
such a facility if I were to write it?

Bob