From: Wilson Bilkovich <wilsonb@...>
Date: 2006-01-01T13:19:27+09:00
Subject: Re: Tuples/Records/Quicky Objects + Read Only Arrays?

On 12/31/05, Christopher Campbell <spamoff.danx@ntlworld.com> wrote:
> Hi,
>
> Does Ruby have a tuple or quicky object mechanism?  I'm new to Ruby and
> have become stuck on how to solve the following.
>
> I'm testing adding items to a container, where each item is a pair of
> strings.  One is a name and another an alias.  As they're added a check
> should be performed to see if they're in the container, etc.
>
> I've been using OCaml for a while, and for this I'd just use a list of
> tuples of strings.  What's the ruby way of doing this?   Iterating over
> a container/array is a doddle, that's not the problem.  The problem is
> really can you have quick pairs without making classes and so on?
>
> While I'm at it, is there a read only array like container?  Don't want
> anyone messing with the internal array, they should not know that what's
> returned is actually the internal representation or fiddle with it.
> Don't care what they do with the elements in the array, only the array
> itself.
>
> class X
>    def initialize
>      @elements = Array.new
>    end
>
>    ...
>
>    def elements
>      @elements.clone
>    end
> end
>
> Returning a clone of an array is fine, just wondered if you could
> "write-protect" stuff in general.
>
>

The Ruby equivalent of a tuple is pretty much an Array, since the
syntax is so lightweight.
a = [1, 2]
a.first == 1
a.last == 2

Possibly due to champagne, I can't think of a built-in object that
behaves the way you want.. but luckily, a quick implementation of it
shouldn't be hard:
class FunBox
  def initialize
    @names = {}
    @aliases = {}
  end

  def <<(pair)
    @names[pair.first] = pair.last
    @aliases[pair.last] = pair.first
  end

  def alias_for_name(n)
    @names[n]
  end

  def name_for_alias(a)
    @aliases[a]
  end
end


irb(main):060:0> f = FunBox.new
=> #<FunBox:0x2e15f00 @aliases={}, @names={}>
irb(main):061:0> f<<['joe', 'jim']
=> "joe"
irb(main):062:0> f.alias_for_name('joe')
=> "jim"
irb(main):063:0> f.name_for_alias('jim')
=> "joe"
irb(main):064:0>

Of course, given that you know OCaml, I'm probably telling you exactly
nothing you don't know.
I'm not aware of a way to freeze instance variables, such that you
couldn't still change them with Object#instance_variable_set