From: Xavier Noria <fxn@...>
Date: 2007-09-21T05:48:44+09:00
Subject: Re: Idiomatic Ruby for Array#extract / Range#length?

On Sep 20, 2007, at 9:41 PM, Rick DeNatale wrote:

> http://talklikeaduck.denhaven2.com/articles/2007/09/20/duck-a-la-range

Well, the fact that the documentation says "must respond to" and "as  
long as" disallows in my view to pass objects that do not respond to  
#<=> and #succ. I think that is clear and unrelated to duck typing.  
Of course that may indicate that the documentation needs a different  
wording, but the current docs are clear and according to them if you  
pass an object that does not respond to #succ to the Range  
constructor the object is invalid, the code is invalid, albeit it may  
run.

About rationals: I claim that the definition of a closed Range in  
Ruby (theoretically) allows for infinite ranges. That's my point. I  
prove that in ruby-talk giving an example.

Now, the example uses the rationals because what I want to show  
follows easily from the fact that Q is bijectable with N, which is a  
basic result in set theory. (See proof in the mailing list.)

Density is always relative to an ordering, and for brevity what I do  
is to change the order using a standard technique which consists of  
defining stuff into one set by transferring it from another through a  
bijection. The fact that the ordenary order of Q makes Q dense is not  
relevant to this discussion at all. You see a class with #<=> and  
#succ that provides an infinite Range.

But that's just a way to support my claim, I could construct another  
thing and show it gives infinite Ranges (again, theoretically). I am  
sure I could simplify the proof for non-mathematicians taking N and  
Inifinity or something close to that.

-- fxn