From: Logan Capaldo <logancapaldo@...>
Date: 2006-12-17T06:48:26+09:00
Subject: Re: Just some Ruby language ideas, comments wanted.

On Sun, Dec 17, 2006 at 04:00:49AM +0900, Devin Mullins wrote:
> Daniel Finnie wrote:
> >How this would work:
> >Currently, the following would default to "i" if the element doesn't exist.
> >[4, 6, 9].fetch(4, "i")
> >This would do the same thing:
> >[4, 6, 9][4].default("i") or [4, 6, 9].fetch(4).default("i")
> I get along fine with:
>   [4, 6, 9].fetch(4)||'i'
> 
> Sure, it has false misses on instances of FalseClass, but I live with 
> the pain. Besides, what if the above array contained nil?
> 
> >This would allow things like:
> >ary = [4, nil, 6, nil]
> >ary.select{|x| x.nil?}[1].set(2)
> >ary # => [4, nil, 6, 2]
> May I suggest:
>   ary.select{|x| x.nil?}[1] = 2
> as a better interface.
> 
> = isn't overridable, but []= is.
> 
> I see more potential in your second thing... Build it as a stand-alone 
> Ruby library first.
> 
> Devin
Here, I'll evenget you started:

% cat view.rb
class ArrayView
  class ArrayIndexRef
    def initialize( array, index )
      @array = array
      @index = index
    end

    def value
      @array[@index]
    end

    def value=(new_value)
      @array[@index] = new_value
    end
  end

  def initialize( array )
    @array = array
    @references = []
  end

  def [](*args)
    if args.length == 1 and args.kind_of? Range or args.length > 1
      @references[*args].map { |x| x.value }
    else
      @references[*args].value
    end
  end

  def []=(index, value)
    @references[index].value = value
  end

  def each
    @references.each do |x|
      yield x.value
    end
  end


  def add_ref( index )
    @references << ArrayIndexRef.new( @array, index )
  end
end


class Array
  def select_view
    r = ArrayView.new( self )
    each_with_index do |item, index|
      r.add_ref( index ) if yield( item ) 
    end
    r
  end
end

a = (1..10).to_a

p a
b = a.select_view { |x| (x % 2).zero? }
b[0] = 42
p a

% ruby view.rb
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1, 42, 3, 4, 5, 6, 7, 8, 9, 10]