From: ahoward <ahoward@...>
Date: 2002-11-15T10:41:45+09:00
Subject: Re: Array#next - Enumerable#next ?

On Fri, 15 Nov 2002, Paul Brannan wrote:

> One problem here is that I can't tell the difference between iterating
> over a nil object in an array (e.g. if I have an array [1, 2, 3, nil,
> 4]) and hitting the end of the array.  This is pretty easy to fix;
> change:
>   return nil
>
> to:
>   return DoneIterating
[snip]

yes.  this is a good idea

[snip]
> A more serious problem here is that code that uses next() is not
> reentrant; if you have a method that is iterating over an array, you'd
> better not call another method that also iterates over that array.
> E.g.:
>
>   def print_array(arr)
>     while (obj = arr.next) != DoneIterating do
>       puts obj
>     end
>   end
>
>   def print_all_ocurrances(arr, x)
>     while (obj = arr.next) != DoneIterating do
>       if x == obj then
>         print "Found object x in array "
>         print_array arr
>         puts
>       end
>     end
>   end
[snip]

i don't view this as a problem - you are viewing the next method as an
iterator, which in definitively is not.  it is an instance method of Array,
and uses instance variables.  i would define Array#next as the the next
object the Array is willing to give me.  this relies on instance variables,
just like Array#size.  if you call a method manipulating Array#size, from
another method manipulating Array#size - would you be suprised that size had
changed?  this is good argument for iterator classes i suppose : one needs a
separte object for tracking state.  however, i've been using that method quite
a bit - it's usefull because it's minimal.

i will check out the links you sent.  thanks.

-a


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