[ruby-talk:01629] Re: Ruby: constructors, new and initialise

The following message is a courtesy copy of an article
that has been posted to comp.lang.misc as well.

Yukihiro Matsumoto <[e-mail]> writes:

> If allocation at `new' uses its arguments, the argument behavior is
> fixed, size of internal buffer in this case.  If you want to make
> subclass of Array, and initialize it by some arguments, you'll meet
> restriction about arguments to `new'.

But say I was implementing a sortable array, where I wanted to
allocate twice the requested storage: the first half to hold the
values, the second half pointers to these values. (Don't ask me why,
because I have no idea. It's a silly example).

     class MyArray < Array
       def MyArray.new(size)
         super(size*2)
       end

       def initialize(size)
         self.[size/2...size] = (0...size/2).to_a
       end
     end

Now, I know I could do this using delegation, but in this case
subclassing seems natural. 

If I hadn't read this thread, I'd expect that MyArray.new(3) would
call MyArray.initialize(6).

Or maybe I wanted an array of pre-computed primes:

     class PrimeArray < Array
       def initialize
         for i in 0...size
           self.[i] = nextPrime
         end
       end
     end


It seems to me that logically, 'new' allocates the storage for the
object, and 'initialize' initializes that store.

I know I must be missing something obvious here. Help!


Regards


Dave