1..5             => [0, 1, 2, 3, 4, 5]
1...5            => [0, 1, 2, 3, 4]
'a'..'d'         => ['a', 'b', 'c', 'd']
'a'...'d'        => ['a', 'b', 'c']
(1..10)  === 10  => true
(1...10) === 10  => false
(1..10)  === 15  => false

while gets # prints lines starting at 'start' and ending at 'end'
  print if /start/../end/
end

# represent a string of 'x's as a Range
class Xs
  include Comparable
  def initialize(n)
    @length = n
  end
  def inspect
    'x' * @length
  end
  # override the following for range utility
  def succ
    Xs.new(@length + 1)
  end
  def <=>(other)
    @length <=> other.length
  end
end
r = Xs.new(3)..Xs.new(6)   #=> xxx..xxxxxx
r.to_a                     #=> [xxx, xxxx, xxxxx, xxxxxx]
r.member?(Xs.new(5))       #=> true

# Ranges can use === comparisons, thus can use case statements
case 12
when 1..10  then   puts "less than 10"
when 10..20 then   puts "between 10 and 20"
when 20..30 then   puts "greater than 20"
end
# outputs => between 10 and 20

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