From: Robert Klemme <bob.news@...>
Date: 2005-10-26T20:47:03+09:00
Subject: Re: Enumerable#build

Martin DeMello wrote:
> 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.)

Looks good.  But,

 - Enumerable is a module... :-)

 - You should add seed as return value.

 - Your first example won't work as Hash#add is nonexistent

An alternative approach would be to reverse the logic and have
Enumerable#populate:

module Enumerable
  def populate(*enum)
    enum = enum.first if enum.size == 1
    enum.each {|*a| add(yield(*a))}
    self
  end
end

class Hash
  def populate(*enum)
    enum = enum.first if enum.size == 1
    enum.each {|*a| send(:[]=, *yield(*a))}
    self
  end
end

>> h={}.populate(1,2,3) {|x| [x, "val #{x}"]}
=> {1=>"val 1", 2=>"val 2", 3=>"val 3"}

What do you think?

Kind regards

    robert