_output.txt

FOO
====================
Hello
World
********************************************************************************
Traced!
Traced!
Hello
World

BAR
====================
hello
world
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Traced!
hello
Traced!
world

FOOBAR
====================
HELLO
WORLD
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
Traced!
HELLO
Traced!
WORLD

FOOBAZ
====================
HeLlo
WoRlD
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Traced!
HeLlo
Traced!
WoRlD

trace_experiment.rb

class Foobar
  def hello; puts "HELLO" end
  def world; puts "WORLD" end
  def speak; hello; world end
end

class Foo
  def hello; puts "Hello" end
  def world; puts "World" end
  def speak; hello; world end
end

class Bar
  def hello; puts "hello" end
  def world; puts "world" end
  def speak; hello; world end
end

class Foobaz
  def hello; puts "HeLlo" end
  def world; puts "WoRlD" end
  def speak; hello; world end
end

module Tracer
  module_function
  def with_tracing; puts "Traced!"; yield end
end

module StaticInstrument
  include Tracer
  def hello; with_tracing { super } end
  def speak; with_tracing { super } end
end

module MetaInstrument
  include Tracer
  %w{hello world}.each do |method_name|
    define_method(method_name) do |*args, &block| 
      with_tracing { super(*args, &block) }
    end
  end
end

puts "FOO", "=" * 20
Foo.new.speak

puts "*" * 80
Foo.prepend StaticInstrument
Foo.new.speak

puts "", "BAR", "=" * 20
Bar.new.speak

puts "%" * 80
Bar.prepend MetaInstrument
Bar.new.speak

puts "", "FOOBAR", "=" * 20
Foobar.new.speak

puts "&" * 80
Foobar.class_eval do
  include Tracer
  alias_method :hello_without_tracing, :hello
  def hello
    with_tracing { hello_without_tracing }
  end

  alias_method :world_without_tracing, :world
  def world
    with_tracing { world_without_tracing }
  end
end
Foobar.new.speak

puts "", "FOOBAZ", "=" * 20
Foobaz.new.speak

def dynamic_tracer_module method_names
  Module.new do
    include Tracer
    method_names.each do |method_name|
      define_method(method_name) do |*args, &block| 
        with_tracing { super(*args, &block) }
      end
    end
  end
end

puts "!" * 40
Foobaz.prepend dynamic_tracer_module %w{hello world}
Foobaz.new.speak