From: Paul Brannan <pbrannan@...>
Date: 2002-09-05T06:31:54+09:00
Subject: Re: School work (no, this isn't a homework problem)

On Thu, Sep 05, 2002 at 06:11:56AM +0900, Peach wrote:
> Well, I'm a Ruby Newbie, so this question should be interesting.
> I somehow talked my professor at school to let me use Ruby instead of C++
> for the algorithm class. Frankly, I find using Ruby much easier than C (and
> it's children). It just makes sense to me.
> In a short amount of time, however, I will have a problem. Pointers will
> very quickly become an integral part of our course study. To continue, I
> would need to do some meaningful pointer work in Ruby. Does anyone know of
> libraries to do such things, or are there other ways? If you could give some
> assistance, I'd be greatly appreciated :)
> I'd like to stick with Ruby, but if the answer is no I'll make do.

Ruby has no pointers.  However, it has references, which are just as
good.

If I write:
  a = 'foo'

then a is a reference to a String object containing the text 'foo'.  You
can think of a reference in Ruby as a pointer with which you cannot do
pointer arithmetic (in C++, you can never modify a reference; Ruby lets
you reassign references, as long as their name doesn't begin with a
capital letter).

It's possible to write a linked list in pure Ruby, but it will be slow.
For example, if I want a singly-linked list that I can only append to
(not very useful), I might write:

  class List
    Node = Struct.new("Node", :next, :value)

    def initialize
      @head = nil
      @tail = nil
    end

    def each(node = @head, &block)
      return if node.nil?
      yield node.value
      each(node.next, &block)
    end

    def push(value)
      if @tail then
        @tail.next = Node.new(nil, value)
        @tail = @tail.next
      else
        @head = @tail = Node.new(nil, value)
      end
    end
  end

I'll leave insertion into the beginning/middle, deletion from the list,
etc. as an exercise for the reader. :)

Paul