smalltalk_bpps.rb

# page 2

=begin
Station>>computePart: aPart
    ^self multiplyPartTimesRate: aPart
Station>>multiplyPartTimesRate: aPart
    ^Part
        amount: aPart amount * self rate
        date: aPart date
=end
class Station
  def compute_part(a_part)
    multiply_part_times_rate(a_part)
  end
  
  def multiply_part_times_rate(a_part)
    # where `rate` is probably an initialized attr on the Station instance
    # where Part has .amount, #amount, and #date defined.
    Part.amount(a_part.amount * rate, date: a_part.date)
  end
end

# page 3 (refactored)

=begin
Part>>* aRate
    ^Part
        amount: amount * aRate
        date: date
Station>>computePart: aPart
    ^aPart * self rate
=end
class Part
  def *(a_rate)
    Part.amount(amount * a_rate, date: date)
  end
end

class Station
  def compute_part(a_part)
    a_part * rate
  end
end
  
# page 22, Composed Method

=begin
Controller>>controlActivity
    self controlInitialize.
    self controlLoop.
    self controlTerminate.
=end
class Controller
  def control_activity
    # where each control_ reference is an instance method on Controller
    control_initialize
    control_loop
    control_terminate
  end
end

# page 24, Constructor Method

=begin
Point class>>r: radiusNumber theta: thetaNumber
    ^self
        x: radiusNumber * thetaNumber cos
        y: radiusNumber * thetaNumber sin
=end
class Point
  def self.x(x_number, y: y_number)
    # ...
  end
  
  def self.r(radius_number, theta: theta_number)
    x(
      (radius_number * thetaNumber).cos,
      y: (radiusNumber * theta_number).sin
    )
  end
end

# page 25, Constructor Parameter Method

=begin
Point class>>x: xNumber y: yNumber
    ^self new
        x: xNumber;
        y: yNumber;
        yourself
=end
class Point
  def self.x(x_number, y: y_number)
    self.new.x(x_number, y: y_number)
  end
end

# refactored
=begin
Point class>>x: xNumber y: yNumber
    ^self new
        setX: xNumber
        y: yNumber
Point>>setX: xNumber y: yNumber
    x := xNumber
    y := yNumber
    ^self
=end
class Point
  def self.x(x_number, y: y_number)
    self.new.set_x(x_number, y: y_number)
  end
  
  def set_x(x_number, y: y_number)
    @x = x_number
    @y = y_number
  end
end

# page 27, Shortcut Constructor Method
=begin
Number>>@ aNumber
    ^Point
        x: self
        y: aNumber
=end
class Number
  def @(a_number)
    Point.x(self, y: a_number)
  end
end