From: matz@... (Yukihiro Matsumoto)
Date: 2001-01-10T15:44:54+09:00
Subject: [ruby-talk:8993] Re: Ranges inside brackets for arrays

Hi,

In message "[ruby-talk:8989] Ranges inside brackets for arrays"
    on 01/01/10, "Hal E. Fulton" <hal9000@hypermetrics.com> writes:

|Only later did I think, "Wait a minute. A 
|range can't go backwards..."
|
|I don't recall seeing an example like this
|documented.
|
|Is the thing in the brackets "not really a
|range" or what? What is going on here?

The truth are:

  * A range enumeration cannot go back, it's upward only.

  * But A range with end point less than start point is valid.

  * Thus 1..-1 is a completely valid range object.

  * Array and String internally convert negative end point into
    size+n, where n is a negative number.

  * So range n..-m is interpreted as n..(size-m), thus works fine (if
    n <= (size-m)).

QED. ;-)
							matz.