7. Dragon ADR Position Change

  • ADR - Architecture Design Records

7.1. Problem

  • Move dragon left by 10 and down by 20

7.2. Option 1

  • Move by relative shifting (left, right, up, down)

>>> dragon.move(left=10, down=20)
>>> dragon.shift(left=10, down=20)
>>> dragon.fly(left=10, down=20)
  • Good: encapsulation, object knows current position and moves

  • Good: easy .move()

  • Bad: to specific .fly(), .shift()

7.3. Option 2

  • Move by relative shifting (left, right, up, down)

>>> dragon.change_position(left=10, down=20)
>>> dragon.position_change(left=10, down=20)
  • Good: encapsulation, object knows current position and moves

  • Bad: to complex for now .change_position(), .position_change()

7.4. Option 3

  • Move by setting absolute position

>>> dragon.move(x=10, y=-20)
>>> dragon.move_to(x=10, y=20)
  • Bad: controller must know current position

7.5. Option 4

>>> dragon.move_x(10)
>>> dragon.move_y(20)
  • Bad: require knowledge of an API

7.6. Option 5

>>> dragon.move(10, 20)
>>> dragon.move_xy(10, 20)
  • Bad: require knowledge of an API

7.7. Option 6

>>> dragon.move((-10, 20))
>>> dragon.move_xy((-10, 20))
  • Bad: require knowledge of an API

7.8. Option 7

>>> dragon.move(dx=10, dy=-20)
>>> dragon.move(horizontal=10, vertical=-20)
  • Good: encapsulation, object knows current position and moves

  • Bad: controller computes final offset

  • Bad: controller must know, right - add to x, left - subtract y

7.9. Option 8

  • move(left, right, up, down)

>>> dragon.move(0, 10, 0, 20)
>>> dragon.move((0, 10, 0, 20))
>>> dragon.move([
...     (0, 10, 0, 20),
...     (0, 10, 0, 20)])
  • Good: there is only one method move() responsible for moving

  • Bad: Python has keyword arguments, so use it

  • Bad: require knowledge of an API

7.10. Option 9

  • move(horizontal, vertical)

  • move by relative offset

>>> dragon.move([
...     (10, 20),
...     (10, 15)])
  • Bad: require knowledge of an API

7.11. Option 9

  • move(x, y)

  • move by setting absolute position

>>> dragon.move([
...     (10, 20),
...     (50, 120),
...     (5)])
  • Bad: require knowledge of an API

7.12. Option 10

>>> dragon.move({'x':50, 'y':120})
>>> dragon.move([
...     {'x':10, 'y':20},
...     {'x':10, 'y':15}])
  • Bad: require knowledge of an API

7.13. Option 11

>>> dragon.move({'left':50, 'down':120})
>>> dragon.move([
...     {'left':50, 'down':120},
...     {'left':50, 'right':120},
...     {'down':50}])
  • Bad: require knowledge of an API

7.14. Option 12

>>> dragon.move({'dx': 10, 'dy': 20})
>>> dragon.move([
...     {'dx': -10, 'dy': 20},
...     {'dx': -10, 'dy': 0}])
>>> dragon.move([
...     {'dx': -10, 'dy': 20},
...     {'dx': -10, 'dy': 20},
...     {'dx': -10, 'dy': 20}])
  • Bad: require knowledge of an API

7.15. Option 13

  • move by setting absolute position

>>> dragon.move([
...     Point(x=10, y=20),
...     Point(x=10, y=15)])

7.16. Option 14

>>> dragon.move([
...     {'direction': 'left', 'distance': 20},
...     {'direction': 'left', 'distance': 10},
...     {'direction': 'right', 'distance': 20}])
  • Bad: require knowledge of an API

7.17. Option 15

>>> x = dragon.x
>>> y = dragon.y
>>> dragon.move(x=x-10, y=y+20)
>>> current = dragon.position
>>> dragon.set_position(x=current.x-10, y=current.y+20)
>>> x = dragon.x - 10
>>> y = dragon.y + 20
>>> dragon.move(x=x, y=y)
>>> dragon.x -= 10
>>> dragon.y += 20
>>> dragon.position_x -= 10
>>> dragon.position_y += 20
  • Bad: encapsulation

  • Bad: require knowledge of an API

7.18. Option 16

>>> dragon.move(x=-10, y=+20)
>>> dragon.move(dx=-10, dy=+20)
>>> dragon.change_position(left=-10, down=20)

7.19. Option 17

>>> dragon.move(direction='left', distance=20)
>>> dragon.move(direction='right', distance=5)
  • Good: explicit

  • Good: verbose

  • Good: extensible

  • Bad: to complex for now

7.20. Option 18

>>> LEFT = 61  # keyboard key code
>>> dragon.move(direction=LEFT, distance=20)
  • Good: explicit

  • Good: verbose

  • Good: extensible

  • Bad: to complex for now

7.21. Option 19

>>> class Direction(Enum):
...     LEFT = 61
>>>
>>>
>>> dragon.move(Direction.LEFT, distance=5)
>>> dragon.move(direction=Direction.LEFT, distance=5)
  • Good: explicit

  • Good: verbose

  • Good: extensible

  • Bad: to complex for now

7.22. Option 20

>>> KEY_BINDING = {
...     'ARROW_UP': dragon.move_up,
...     'ARROW_DOWN': dragon.move_down,
...     'ARROW_LEFT': dragon.move_left,
...     'ARROW_RIGHT': dragon.move_right}
>>>
>>>
>>> def action(key, time):
...     return KEY_BINDING.get(key)(time)
>>>
>>>
>>> action('ARROW_UP', 5)
  • Good: explicit

  • Good: verbose

  • Good: extensible

  • Bad: to complex for now

7.23. Option 21

>>> dragon.move_left(10)
>>> dragon.move_right(10)
>>> dragon.move_upright(10)
>>> dragon.move_downright(10)
>>> dragon.move_downleft(10)
>>> dragon.move_upleft(10)
>>> dragon.move_left_down(10, 20)

Good, because:

>>> game.bind_key(Key.LEFT_ARROW, dragon.move_left)
>>> game.bind_key(Key.RIGHT_ARROW, dragon.move_right)

Bad, because:

>>> db.execute_select(SQL)
>>> db.execute_select_where(SQL)
>>> db.execute_select_order(SQL)
>>> db.execute_select_limit(SQL)
>>> db.execute_select_order_limit(SQL)
>>> db.execute_select_where_order_limit(SQL)
>>> db.execute_insert(SQL)
>>> db.execute_insert_values(SQL)
>>> db.execute_alter(SQL)
>>> db.execute_alter_table(SQL)
>>> db.execute_create(SQL)
>>> db.execute_create_table(SQL)
>>> db.execute_create_database(SQL)

Why not?:

>>> db.execute(SQL)

Use Case:

>>> read_csv('iris.csv', 'utf-8', ';', True)
>>> read_csv_with_encoding('iris.csv', 'utf-8')
>>> read_csv_with_delimiter('iris.csv', ';')
>>> read_csv_with_delimiter_encoding('iris.csv', ';', 'utf-8')
>>> read_csv_with_delimiter_encoding_verbose('iris.csv', ';', 'utf-8', True)
>>> read_csv('iris.csv')
...     .withEncoding('utf-8')
...     .withDelimiter(';')
...     .withVerbose(True)
>>> file = CSV()
>>> file.set_file('iris.csv')  # encapsulation?!
>>> file.set_encoding('utf-8')
>>> file.set_delimiter(';')
>>> file.set_verbose(True)
>>> read_csv('iris.csv', encoding='utf-8', delimiter=';', verbose=True)
>>> read_csv('iris.csv',
...          encoding='utf-8',
...          delimiter=';',
...          verbose=True)
  • Bad: not extensible

  • Bad: to complex for now

7.24. Decision

>>> dragon.move(left=10, down=20)
  • Good: easy

  • Good: verbose

  • Good: extensible

Alternative:

>>> dragon.change_position(left=10, down=20)
  • Good: consistent with set_position()

  • Good: verbose

  • Good: extensible

  • Bad: to complex for now