method_missing.rb

# This extends the Array class with a special method called each_[insert integer here]
# For example, each_1 invokes the block for every single element in an array, each_2 invokes the block for
# each pair, each_3 for triples, so on and so forth. This is a purely educational example of using 
# metaprogramming to replicate functionality using patterns rather hard coding a new method for each 
# new case you need to account for.
class Array

  def method_missing(meth, *args, &block)
    if meth.to_s =~ /^each_(\d+)$/
      run_each_by_num($1.to_i, &block)
    else
      super
    end 
  end 
  
  # Iterates through self in increments of num, yielding the current
  # range as an array
  def run_each_by_num(num, &block)
    self.inject(0) do |curr|
      break if curr >= self.length
      yield self[curr..(curr - 1 + num)]
      curr += num 
    end 
  end 
end

a = Array.new([2,3,4,5,8,0,1,3,4,5])

# Outputs: [2] [3] [4] [5] [8] [0] [1] [3] [4] [5]
# Note: the preceding and following examples ignore newlines.
a.each_1 do |x| 
  puts "#{x}"
end

# Outputs: [2, 3, 4, 5] [8, 0, 1, 3] [4, 5]
a.each_4 {|x| puts "#{x}"}

# Outputs: [2, 3, 4, 5, 8] [0, 1, 3, 4, 5]
a.each_5 do |x| 
  puts "#{x}"
end

# Outputs: [2, 3, 4, 5, 8, 0, 1, 3, 4] [5]
a.each_9 do |x| 
  puts "#{x}"
end