raganwald
Saturday, July 05, 2008
  Sneak Peek: Unhygienic Rewriting Ruby by Example

def test_unhygienic_andand
  andand = Unhygienic.from {
    __to_receiver.andand.__to_message(__splat_parameters)
  }.to {
    lambda { |andand_temp|
      andand_temp.__to_message(__splat_parameters) if andand_temp
    }.call(__to_receiver)
  }
  assert_equal(
    'Hello' + ' World', 
    with(andand) do
        'Hello'.andand + ' World'
    end
  )
  assert_nil(
    with(andand) do
        nil.andand + ' World'
    end
  )
end
Let’s take a closer look:

Rewrite::With.expand(andand) do
  class Funky
    def hello_world
      'Hello'.andand + ' World'
    end
  end
end
produces:

class Funky
  def hello_world
    lambda { |andand_temp| 
        (andand_temp + " World") if andand_temp 
    }.call("Hello")
  end
end
As you can probably deduce, it’s unhygienic: Variables like andand_temp shadow variables declared elsewhere. This is a problem if you fail to choose a sufficiently obfuscated name or—more likely—nest constructions like #andand.

Both the Classically Metaprogrammed and the Sexp-Rewriting versions of #andand avoid this problem.

Next step: Better hygiene.
 

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