caller.rb

class Caller
  def self.exec_before( method_name)
    @@before = method_name 
  end

  def self.exec_after( method_name )
    @@after = method_name
  end

  def execute( &code )
    method(@@before).call if defined? @@before
    code.call
    method(@@after).call if defined? @@after
  end
end

class Executor < Caller

  exec_before( :say_hello )
  exec_after( :say_bye )


  def say_hello
    puts "Hello, I'm here!"
  end

  def say_bye
    puts "Good bye!"
  end
end

exec = Executor.new

exec.execute do 
  puts "I do my job"
end

# Hello, I'm here!
# I do my job
# Good bye!