From: Konrad Meyer <konrad@...>
Date: 2007-11-19T11:10:51+09:00
Subject: Re: Open-ended ranges?

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Quoth Clifford Heath:
> Folk,
>=20
> I found Sean Russell's 2001 posting on this subject, and had a play with=
=20
creating
> open ranges using of class instances - interesting to find you can even d=
o=20
this!
>=20
> 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 fo=
r=20
the
> reason I expected. There seems to be some magic inside MRI that prevents =
it.
>=20
> Like if I define:
>=20
> class End
> 	attr_reader :e
> 	def initialize(e)
> 		@e =3D e
> 	end
> 	def <=3D>(other)
> 		@e <=3D> other.e
> 	end
> 	def succ
> 		@e && @e.succ
> 	end
> end
>=20
> Then I can create the following range: End.new(1) .. End.new(4)
> but not this: End.new(1) .. End.new(nil)
>=20
> 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).
>=20
> Now add puts "#{@e.to_i} <=3D> #{other.e}"; into the "<=3D>" method, and
> Range "knows" that's not ok... when to my mind it should be ok if the
> previous version was.
>=20
> 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 advertise=
d,
> it didn't seem worth pursuing.
>=20
> What do you think?
>=20
> Clifford Heath.

Then again, there is this already:

irb(main):001:0> 0..(1.0/0)
=3D> 0..Infinity

HTH,
=2D-=20
Konrad Meyer <konrad@tylerc.org> http://konrad.sobertillnoon.com/

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