Range

A Range represents an interval—a set of values with a start and an end. Ranges may be constructed using the s..e and s...e literals, or with Range::new. Ranges constructed using .. run from the start to the end inclusively. Those created using ... exclude the end value. When used as an iterator, ranges return each value in the sequence.

   (-1..-5).to_a      #=> []
   (-5..-1).to_a      #=> [-5, -4, -3, -2, -1]
   ('a'..'e').to_a    #=> ["a", "b", "c", "d", "e"]
   ('a'...'e').to_a   #=> ["a", "b", "c", "d"]

Ranges can be constructed using objects of any type, as long as the objects can be compared using their <=> operator and they support the succ method to return the next object in sequence.

   class Xs                # represent a string of 'x's
     include Comparable
     attr :length
     def initialize(n)
       @length = n
     end
     def succ
       Xs.new(@length + 1)
     end
     def <=>(other)
       @length <=> other.length
     end
     def to_s
       sprintf "%2d #{inspect}", @length
     end
     def inspect
       'x' * @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

In the previous code example, class Xs includes the Comparable module. This is because Enumerable#member? checks for equality using ==. Including Comparable ensures that the == method is defined in terms of the <=> method implemented in Xs.