Examples of Horizontal Reuse
Java implementation using interfaces.
Java implementation using interfaces plus the delegation pattern.
Ruby implementation using mixins.
Ruby implementation using traitor. This doesn't actually seem to work on my machine.
PHP 5.4+ implementation using traits.
Perl 5 implementation using Moose.
Perl 5 implementation using Moo, a small OO framework that promises "almost -- but not quite -- two thirds of Moose". It's almost line-by-line identical to the Moose implementation.
Perl 5 implementation using mop, Steven Little's reimplementation of a subset of Moose, intended for inclusion in the Perl core.
Perl 6 implementation using the language's native roles.
Python example using multiple inheritance from abstract base classes.
Scala implementation using the language's native traits.
I'd appreciate contributions for any programming languages I've missed; in particular any where this sort of thing can be done especially elegantly.