sequence

gistfile1.rb

#
# This class represents a sequence of numbers characterized by the three
# parameters from, to, and by. The numbers x in the sequence obey the
# following two constraints:
#
# from <= x <= to
# x = from + n*by, where n is an integer
#
class Sequence
  # This is an enumerable class; it defines an each iterator below.
  include Enumerable # Include the methods of this module in this class
  # The initialize method is special; it is automatically invoked to
  # initialize newly created instances of the class
  def initialize(from, to, by)
    # Just save our parameters into instance variables for later use
    @from, @to, @by = from, to, by # Note parallel assignment and @ prefix
  end
  # This is the iterator required by the Enumerable module
  def each
    x = @from # Start at the starting point
    while x <= @to # While we haven't reached the end
    yield x # Pass x to the block associated with the iterator
    x += @by # Increment x
  end

  # Define the length method (following arrays) to return the number of
  # values in the sequence
  def length
    return 0 if @from > @to # Note if used as a statement modifier
    Integer((@to-@from)/@by) + 1 # Compute and return length of sequence
  end

  # Define another name for the same method.
  # It is common for methods to have multiple names in Ruby
alias size length # size is now a synonym for length

  # Override the array-access operator to give random access to the sequence
  def[](index)
    return nil if index < 0 # Return nil for negative indexes
    v = @from + index*@by # Compute the value
    if v <= @to # If it is part of the sequence
      v # Return it
    else # Otherwise...
      nil # Return nil
    end
  end

  # Override arithmetic operators to return new Sequence objects
  def *(factor)
    Sequence.new(@from*factor, @to*factor, @by*factor)
  end
  def +(offset)
    Sequence.new(@from+offset, @to+offset, @by)  
  end
end