Endless Range

If you have a Range that you want to extend infinitely in either direction, just simply leave it blank.

Here's a simple example:

def age_category(age)
  case age
  when (...0)
    "unborn"
  when (0..12)
    "youngling"
  when (13..17)
    "teenager"
  when (18..64)
    "adult"
  when (65..)
    "old"
  end
end

>> age_category    0 => "youngling"
>> age_category   13 => "teenager"
>> age_category   18 => "adult"
>> age_category   65 => "old"
>> age_category  999 => "old"
>> age_category -999 => "unborn"

In a situation like this it's nice to extend infinitely, rather than having to come up with some kind of arbitrary cutoff age like 100, that could in rare cases cause problems.

H/T Matt Polito for showing me this.