From: Joel VanderWerf <vjoel@...>
Date: 2003-01-18T07:48:36+09:00
Subject: Re: Accessing Infinity

Kent Dahl wrote:
> Joel VanderWerf wrote:
> 
>>Well, Ruby's floating point number system does include two infinities,
>>so I guess it's reasonable to compare with them...
> 
> 
> This might sound a bit pedantic but:
> 
> Ruby doesn't provide the two infinitive numbers. The underlying floating
> point routines do. So you don't have two infinities, since any Float
> object can be infinite. You can have an infinite number of infinities. 
> 
> $ irb
> irb(main):001:0> a = 1.0/0
> Infinity
> irb(main):002:0> b = 1.0/0
> Infinity
> irb(main):003:0> a.id
> 537929428
> irb(main):004:0> b.id
> 537915848
> irb(main):005:0> a.equal? b
> false

But...

(1.2).equal?(1.2)           # ==> false
(10**100).equal?(10**100)   # ==> false

Does that mean there are an infinity of googols?

I don't think #equal? is the mathematically correct comparison for 
numbers that may be implemented as heap allocated entities. That's the 
job of #==.

> So the only use for the Infinity constants I can see, is for clarity
> (and space conserving) when you explicitly assign Infinity to more than
> one variable. Creating them for comparison is just plain wasteful, as it
> is one more object in ObjectSpace and a more complicated comparison,
> having to look into two objects instead of one. 

That's why I define a constant... (and also so I can use it in case 
statements, though I'm not sure I ever have, so I will shut up now :-)