# Solution to the triple dispatch exercise

# NOTE: This example is a bit contrived, because we don't actually use the
# values x, y, and z. In general, the "base cases" of a multimethod (the third
# level in this case) will behave differently based on the classes that the
# dispatched arguments are determined to have (e.g., by calling different
# methods or by doing different computation altogether).

# Kick off the process for a given x, y, and z
def f(x, y, z)
  puts x.f(y, z)
end

class A
  # The first dispatch level
  def f(y, z)
    # x is self, and must be an instance of A
    y.f_A(self, z)
  end

  # The second dispatch level
  def f_A(x_A, z)
    # x (now named x_A) was an instance of A
    # y is self, which must be an instance of A
    z.f_AA(x_A, self)
  end
  def f_B(x_B, z)
    # x (now named x_B) was an instance of B
    # y is self, which must be an instance of A
    z.f_BA(x_B, self)
  end

  # The third dispatch level
  def f_AA(x_A, y_A)
    # x (now named x_A) was an instance of A
    # y (now named y_A) was an instance of A
    # z is self, which must be an instance of A
    "(A, A, A)"
  end
  def f_AB(x_A, y_B)
    # x (now named x_A) was an instance of A
    # y (now named y_B) was an instance of B
    # z is self, which must be an instance of A
    "(A, B, A)"
  end
  def f_BA(x_B, y_A)
    # x (now named x_B) was an instance of B
    # y (now named y_A) was an instance of A
    # z is self, which must be an instance of A
    "(B, A, A)"
  end
  def f_BB(x_B, y_B)
    # x (now named x_B) was an instance of B
    # y (now named y_B) was an instance of B
    # z is self, which must be an instance of A
    "(B, B, A)"
  end
end

class B
  # The first dispatch level
  def f(y, z)
    # x is self, which must be an instance of B
    y.f_B(self, z)
  end

  # The second dispatch level
  def f_A(x_A, z)
    # x (now named x_A) was an instance of A
    # y is self, which must be an instance of B
    z.f_AB(x_A, self)
  end
  def f_B(x_B, z)
    # x (now named x_B) was an instance of B
    # y is self, which must be an instance of B
    z.f_BB(x_B, self)
  end

  # The third dispatch level
  def f_AA(x_A, y_A)
    # x (now named x_A) was an instance of A
    # y (now named y_A) was an instance of A
    # z is self, which must be an instance of B
    "(A, A, B)"
  end
  def f_AB(x_A, y_B)
    # x (now named x_A) was an instance of A
    # y (now named y_B) was an instance of B
    # z is self, which must be an instance of B
    "(A, B, B)"
  end
  def f_BA(x_B, y_A)
    # x (now named x_B) was an instance of B
    # y (now named y_A) was an instance of A
    # z is self, which must be an instance of A
    "(B, A, B)"
  end
  def f_BB(x_B, y_B)
    # x (now named x_B) was an instance of B
    # y (now named y_B) was an instance of B
    # z is self, which must be an instance of A
    "(B, B, B)"
  end
end

# Solution to the bonus exercise, using reflection

def g(x, y, z)
  puts "(" + x.class.to_s + ", " + y.class.to_s + ", " + z.class.to_s + ")"
end