Infinite ranges in C#

Jonas Elfström — Tue, 20 Oct 2009 20:41:00 +0200

I recently learned that C# is compliant with the IEEE 754-1985 for floating point arithmetics. That wasn't a big surprise but that division by zero is defined as Infinity in it was! It actually kind of bothers me that I didn't know this.

In mathematics division by zero is undefined for real numbers but I guess Infinity is a more pragmatic result. Or as a friend put it "IEEE stands for Institute of Electrical and Electronics Engineers not Institute of Mathematics"

1234	double n = 1.0;n = n / 0;if (n > 636413622384679305) System.Console.WriteLine("Yes it certainly is!");

This C# code does not throw an exception, it simply leaves n defined as Infinity and a line written to the console.

Ruby is also IEEE 754-1985 compliant. It even lets you define infinite ranges.

Infinity=1.0/0
=>Infinity
(1..Infinity).include?(162259276829213363391578010288127)
=> true
(7..Infinity).step(7).take(3).inject(&:+) # 7+14+21
=> 42

I can't say I see very much use of this but it brings a kind of completeness to the handling of infinities. Unfortunately it seems we don't get that in C# out of the box because Enumerable.Range takes <int>,<int> as parameters and there's no Infinity definition for int. That's unless someone wrote a generic Range class. Turns out none other than Jon Skeet did in his MiscUtil. Dowload MiscUtil and then by using MiscUtil.Collections; you can:

double n = 1.0;
var infinity = n / 0;
var r = new Range<double>(0, infinity);
if (r.Contains(4711))
  System.Console.WriteLine("Yes it certainly does!");
var sum = r.Step(7.0).Take(3).Sum();

And guess what, it works like a charm! 4711 is part of positive infinity and sum is 42.0 and all is good.

Edit

There's also a couple of predefined constants. Thanks to Eric for pointing that out.

12	var r = new Range<double>(7, System.Double.PositiveInfinity);var sum = r.Step(7.0).Take(3).Sum();

"Infinite ranges in C#" by Eric Lippert

Wed, 21 Oct 2009 00:13:35 +0200

Nice!

Of course you could just use the predefined constants System.Double.PositiveInfinity and System.Double.NegativeInfinity; no need to define your own.

Alice, Bob and Mallory: Infinite ranges in C#

Infinite ranges in C#

"Infinite ranges in C#" by Eric Lippert