From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2006-07-10T18:45:11+09:00
Subject: Re: Enumberable fails for class Subclass < Array; def enum...

Laza wrote:
> Array includes Enumerable. But when a subclass of Array redefines
> each(), then Enumerable still refers to the original Array.each(). Why
> is that?
> For example:
> 
> class RangeUnion < Array
>     def each
>         super{|x|  x.each{|i| yield i}  }
>     end
> end
> 
> # u = RangeUnion[1..3, 11..13, "a".."c"]
> # u.each{|x| print "#{x} "}       # THIS WORKS
> # #=> 1 2 3 11 12 13 a b c
> #
> # u.collect{|x| x}                # THIS FAILS!!!
> # #=> [1, 2, 3, 11, 12, 13, "a", "b", "c"]   # expected
> # #=> [1..3, 11..13, "a".."c"]               # actual
> 
> In the example above, each() is redefined. But collect() does not use
> the redefined each()!!! It uses Array.each(). Subclassing from some
> other class works fine:
> 
> class RangeUnion < NotAnArray; ... # gives expected result
> 
> It seems that Enumerable is hardwired (built in) in Array. But subclass
> should be able to override it. Why isn't that possible?

I've experienced problems myself when trying to redefine some of 
Enumerable's methods. Apparently Array uses its own #collect and #map 
methods, plus some others. Maybe if you explicitly re-include Enumerable 
into your subclass?


Cheers,
Daniel