From: "Brett H. Williams" <brett_williams@...>
Date: 2003-04-26T01:13:29+09:00
Subject: Re: freezing Array/Hash length

On Apr 25, gabriele renzi wrote:
> Hi gurus & nubys,
> I just felt in a problem where I'd like to have a fixed size
> Array/Hash [1]. 
> 
> BTW if I simply freeze my object I can't change the length, but
> neither the object , so I have to do something like this
> 
> def add_myarr(x)
> @myarr.push x if @myarr.last < MAX_LENGTH
> end
> 
> Tjhis works fine cause I just put objects in the array trough this
> method, but looks ugly, and I suppose that must be a better way to do
> this. 
> Anyone out there could help me ?

I'm not sure but my first post didn't make it apparently...


First I don't think myarr.last < MAX_LENGTH does what you want:
irb(main):001:0> ar = ["foo", "bar"]
["foo", "bar"]
irb(main):002:0> MAX_LENGTH = 2
2
irb(main):003:0> ar.last < MAX_LENGTH
TypeError: failed to convert Fixnum into String
    from (irb):3:in `<=>'
    from (irb):3:in `<'
    from (irb):3

I think you want to check size, not the last element.

At any rate, why not:

class FixedArray < Array
  def push(x)
    super(x) if size() < MAX_LENGTH
  end
  def []=(idx,x)
    super(idx,x) if idx < MAX_LENGTH - 1
  end
end

You'd still have to be careful of other methods that might increase the length
of an array.

> [1] damn, I always wanted a variable length array when using java..

like a Vector?