Some systems provide a way to query for a capability: COM has
QueryInterface, Racket dynamic-require, Emacs fboundp, and so on. When
such a query method is available, you can simply ask for the thing you
need or prefer. If it's available, great. If not, act appropriately:
Fail, or use your own "back fill" that does something similar or is just
a no-op, or whatever is appropriate.
[IMHO this is more sensible than using version numbers as proxies for
the thing you really care about. Especially lawyerly systems like
so-called semantic versioning. But I digress. :)]
The Racket flavor is something like the following. Let's say
some/module/path maybe has a new fribble function. If that's not
present, or if indeed that whole module isn't even installed, we want to
use our own our-fribble function as a default:
(define (our-fribble _x)
'some-default-value)
(define fribble
(with-handlers ([exn:fail? (λ _ our-fribble)])
(dynamic-require 'some/module/path
'fribble)))
For example, I use this and also Emacs' fboundp in Racket Mode, to
support various versions of Racket and Emacs, both.
I don't know if/how this would help your case. Their API uses the
futzing-with-version-numbers approach. Even so, _maybe_ you'd want to
localize the version number checks in one module, which provides the
functions for your other code to use? The functions will end up being
either the real broker thing, or your own default.
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