http://twitter.com/zombidev/status/164484915059113984

composition_vs_inheritance.md

#include and #extend have same effect on instances as inheritance

Let's say we have this

module A; end
module B; end
class C; end
class D < C; end

Then we modify instance

d = D.new
D.send(:include, A)
d.extend(B)
d_meta = class << d; self; end

Lets see what we got (method dispatch lookup table)

d.class.ancestors
=> [D, A, C, Object, Kernel, BasicObject]

d_meta.ancestors
=> [B, D, A, C, Object, Kernel, BasicObject]

So it's all up to how and what structure you see

and to me, benefits of composition over inheritance is that it doesn't modify object dispatch hierarchy.

PS: pls comment here.

Well, the statement was "it's a good hack, but bad practice".
Works fine on small scopes, but once grows it becomes harder to read thus understand the code, given this as a normal practice.
Debugging is hard because it's not quite obvious why it's doing one thing instead of another and that's only because at some point of call stack an object got extended with a module.

Don't get me wrong, it works. But at certain point it's like "magic" )

I don't do enough obscure programming

well, that's how you start! ;)