From: Gavin Kistner <gavin.kistner@...>
Date: 2008-03-27T05:02:28+09:00
Subject: Re: Recent changes in Range#step behavior

From: Dave Thomas [mailto:dave@pragprog.com] 
> The anomaly is ranges of floats, which you aren't allowed to iterate  
> anyway. In that case, member? becomes a comparison that the argument  
> is between the limit, because conceptually the range (1.0..2.0)  
> contains the infinite number of real values between 1 and 2.

I've occasionally found it convenient to use a single Range of Time
values, to be able to determine if a time falls in the middle of them. A
range of Times would not, I think, be considered discrete.

I would be sad (and confused) if this behavior changed:

irb(main):006:0> t1 = Time.now
=> Wed Mar 26 13:59:15 -0600 2008
irb(main):007:0> t2 = t1 + 10
=> Wed Mar 26 13:59:25 -0600 2008
irb(main):008:0> t3 = t1 + 5.5
=> Wed Mar 26 13:59:21 -0600 2008
irb(main):009:0> (t1..t2).include?( t3 )
=> true

...despite the fact that Time#succ is defined and happens to step
forward 1 second at a time.

I ask for validating arguments to the claim that a range is a set of
discrete elements. I contend that it is only discrete once it is
actually expanded/iterated. It seems more appropriate to have
my_range.to_set.include?( foo ) when you truly want to talk about set
membership.