1  
   2  require 'enumerator'
   3  
   4  # Returns an object of the argument's class with each_slice of 2 switched around.
   5  # Works on any object that mixes in #each
   6  # 
   7  # Examples:
   8  # switch_around("foo!")       #=> of!o
   9  # switch_around((1..10).to_a) #=> [2, 1, 4, 3, 6, 5, 8, 7, 10, 9]
  10  def switch_around(data)
  11    switched_data = data.class.new
  12    
  13    # When appending to a string ints will have #chr called on them, so protect against 
  14    # error about sending a message to nil. b will only be nil when the  collection is 
  15    # an odd length. Of course, this creates a bug. For example we could have an Array with 
  16    # embedded nils, so we must also check if it is a String (again...)
  17    switch_proc = lambda do |a,b|
  18      switched_data << b unless b.nil? and data.is_a?(String)
  19      switched_data << a
  20    end
  21    
  22    # String#each enumerates over lines, so we must change it to enumerate over bytes.
  23    if data.is_a?(String)
  24      data.to_enum(:each_byte).each_slice(2) { |a,b| switch_proc.call(a, b) }
  25    else
  26      data.each_slice(2) { |a,b| switch_proc.call(a,b) }
  27    end
  28    
  29    switched_data
  30  end