From: Matt Armstrong <matt+dated+1007960706.3ec839@...>
Date: 2001-11-10T14:05:12+09:00
Subject: [ruby-talk:24822] Re: Strange behaviour of Array#[]

matz@ruby-lang.org (Yukihiro Matsumoto) writes:

> Hi,
>
> In message "[ruby-talk:24773] Re: Strange behaviour of Array#[]"
>     on 01/11/10, "Lyle Johnson" <ljohnson@resgen.com> writes:
>
> |> I believe it's for consistency with Strings:
> |
> |This is still pretty squirrelly to me, but hey, it's not my language ;)
>
> For these methods, each index points at the edge between elements.
>
> Suppose we have array = [0, 1, 2, 3],
>
>    -4  -3  -2  -1
>     +---+---+---+---+
>     | 0 | 1 | 2 | 3 |
>     +---+---+---+---+
>     0   1   2   3   4
>
> when the index is not pointing existing edge, array[idx, n] returns
> nil (in this case, idx < -4 or 4 < idx).
>
> Index 4 points the last edge of the array, so it does return a
> subarray, which is an empty array since there's no element after the
> last edge.

Does this make some programming tasks easier?

I now understand the "mental picture" that defines the behavior, but
not the "why."  :-)


-- 
matt