From: Martin DeMello <martindemello@...>
Date: 2005-10-26T20:02:03+09:00
Subject: Enumerable#build

class Enumerable
  def build(seed)
    each {|i|
      seed.add(yield i)
    }
  end
end

and 

Array#build == Array#<<
Hash#build(k,v) == Hash#[]
etc

So you could say [1,2,3].build({}) {|i| [i, 1]} for the question that
prompted the to_hash thread, but also, in general, you can collect into
non-array structures (binary trees, e.g.) as long as they implement a
suitable #add method.

(Of course, you can do ary.inject(seed) {|i| seed.add(f(i)); seed} right
now but a #build method makes the common case pretty.)

martin