From: al_batuul <al_batuul@...>
Date: 2007-11-19T21:44:36+09:00
Subject: Re: Open-ended ranges?

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Dear Clifford,
   
  Defining an open-end class is a great idea;  the rang from 1..nil or 0 to nil could help now, I suggest you add different types of parameters to the class such as time.
   
  all the best,
  al_batuul
   

Clifford Heath <no@spam.please.net> wrote:
  Folk,

I found Sean Russell's 2001 posting on this subject, and had a play with creating
open ranges using of class instances - interesting to find you can even do this!

What I really want is to be able to define ranges like (1..nil), which is an
open-ended range starting from 1. Of course this doesn't work, but not for the
reason I expected. There seems to be some magic inside MRI that prevents it.

Like if I define:

class End
attr_reader :e
def initialize(e)
@e = e
end
def <=>(other)
@e <=> other.e
end
def succ
@e && @e.succ
end
end

Then I can create the following range: End.new(1) .. End.new(4)
but not this: End.new(1) .. End.new(nil)

Ok, perhaps that's fair enough. But inside class End, replace all
references to @e by @e.to_i (just for the experiment), and it works
(at least, it bitches that 0 is less than 1, but use
End.new(-1) .. End.new(nil)
and it's ok).

Now add puts "#{@e.to_i} <=> #{other.e}"; into the "<=>" method, and
Range "knows" that's not ok... when to my mind it should be ok if the
previous version was.

I haven't taken this any further yet. Until I know that some internal
magic isn't going to stop me making a Range class that works as advertised,
it didn't seem worth pursuing.

What do you think?

Clifford Heath.



       
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