Deeper into blocks

blocks.rb

# Blocks are a way of "injecting" code to run in the context of the original method.
# Side note: we can open an existing class and add methods.
# Let's make the String class awesome, don't worry about the blocks yet

class String
  def hax0rify
    replac0rs = {
      'o' => '0',
      'a' => '4'
    }
    h4x0r3d = self.downcase
    replac0rs.each do |original, replacement|
      h4x0r3d.gsub!(original, replacement)
    end
    h4x0r3d.chars.map { |c| rand(10) > 5 ? c.upcase : c }.join
  end
end

foo = "Hello my fellow Americans.".hax0rify

foo # => "Hell0 mY FElL0w 4meriC4nS."

# This is great, but what if we want the user to decide what the replacement hash should be?
# We can pass the replacement hash to the user for modification by using yield
# The user "catches" the hash through the pipes and modifies it

class String
  def hax0rify # !> method redefined; discarding old hax0rify
    replac0rs = {
      'o' => '0',
      'a' => '4'
    }
    yield replac0rs
    h4x0r3d = self.downcase
    replac0rs.each do |original, replacement|
      h4x0r3d.gsub!(original, replacement)
    end
    h4x0r3d.chars.map { |c| rand(10) > 5 ? c.upcase : c }.join
  end
end

foo = "Hello my fellow Americans.".hax0rify do |replacement_hash|
  replacement_hash['e'] = '3'
  replacement_hash['l'] = '1'
end

foo # => "H3110 mY F3110w 4M3ric4ns."

# So the object replac0rs INSIDE the method, gets passed to the block as replacement_hash and the object is modified
# when the block returns, the modified object is used INSIDE THE METHOD. HOLY CRAP THIS IS SOME POWERFUL SHIT!

# Iterators like each and map work much the same way
# Let's make our own, this time we'll pass two values to the block
# Ignore the horrible duplication of existing methods

class String
  def modify_each_letter_with_index
    new_string = ''
    i = 0
    while i < self.length
      new_string << yield(self[i].chr, i)
      i += 1
    end
    new_string
  end
end

foo = "Hello my fellow Americans.".modify_each_letter_with_index do |letter, index|
  if index % 3 == 0
    letter.upcase
  else
    letter * 2
  end
end

foo # => "HeellLoo  Myy  FeellLooww AAmmErriiCaannS.."