Improve documentation for inheritance, basic attribute access

docsrc/_static/custom.css

@@ -12,4 +12,5 @@ dl.object > dt, dl.data > dt, dl.function > dt, dl.method > dt, dl.attribute > d
 
 .body a {
     text-decoration: underline;
-}
+}
+

docsrc/examples/arrows.rst

@@ -5,10 +5,19 @@ Arrows
 
 This game demonstrates how to have objects that:
 
-    * Respond to `'typing'` and `'done typing'` events to "keep moving" until a key is released (even when multiple keys are pressed)
+    * Respond to ``'typing'`` and ``'done typing'`` events to "keep moving" until a key is released (even when multiple keys are pressed)
     * Moving objects in sync
 
 
+The major trick is to have a field (e.g., ``active``) that gets set to ``True`` during the ``'typing'`` event
+and set to ``False`` during the ``'done typing'`` event. Then, in a ``updating`` event, you can check if the field
+is ``True`` and move the object accordingly.
+
+For handling left and right keys, you need two boolean fields. For all four direction keys, you would need four boolean fields.
+An alternative solution is to use a string field that gets set to ``'left'``, ``'right'``, ``'up'``, or ``'down'`` during the ``'typing'`` event,
+and then set to ``'none'`` during the ``'done typing'`` event. Then, in the ``updating`` event, you can check the value of the field
+and move the object accordingly.
+
 .. tabs::
 
     .. group-tab:: Dataclasses

docsrc/examples/inheritance.rst

@@ -0,0 +1,23 @@
+.. _inheritance:
+
+Extending DesignerObjects
+=========================
+
+This game demonstrates how to have:
+
+* A ``DesignerObject`` that has additional extra fields using inheritance
+
+By inheriting from a constructor for a ``DesignerObject``, you can add additional fields.
+One drawback is that when calling the constructor for your new class, you must pass in the field as a keyword argument.
+This just means you put the name of the field in front of the value you want to pass in.
+
+In this example, we inherit ``MovingEmoji`` from ``Emoji`` so that we can add ``speed`` and ``direction`` fields.
+Now, we can freely access ``world.dragon.speed`` the same way we could previously access ``world.dragon.x`` or
+``world.dragon.height``.
+
+.. tabs::
+
+    .. group-tab:: Dataclasses
+
+        .. literalinclude:: ./inheritance/inheritance_dataclass.py
+            :language: python

docsrc/examples/inheritance/inheritance_dataclass.py

@@ -0,0 +1,45 @@
+from designer import *
+from dataclasses import dataclass
+
+
+# Note that we have (Emoji) after the name of the new class!
+class MovingEmoji(Emoji):
+    """ An emoji that can move in a direction at a speed """
+    speed: int
+    direction: int
+
+@dataclass
+class World:
+    dragon: MovingEmoji
+
+def create_dragon() -> MovingEmoji:
+    """ Create a dragon with initial speed 1, moving to the right"""
+    return MovingEmoji('🐉', speed=1, direction=0)
+
+def create_world() -> World:
+    """ Create a world with a dragon in it """
+    return World(create_dragon())
+
+def accelerate_dragon(world: World, key: str):
+    """ Pressing up or down increases or decreases the dragon's speed """
+    if key == 'up':
+        world.dragon.speed += 1
+    elif key == 'down':
+        world.dragon.speed -= 1
+
+def spin_dragon(world: World, key: str):
+    """ Pressing left or right increases or decreases the dragon's direction """
+    if key == 'left':
+        world.dragon.direction -= 10
+    elif key == 'right':
+        world.dragon.direction += 10
+
+def move_dragon(world: World):
+    """ Move the dragon forward in its current direction based on its speed """
+    move_forward(world.dragon, world.dragon.speed, world.dragon.direction)
+
+when('starting', create_world)
+when('updating', move_dragon)
+when('typing', spin_dragon)
+when('typing', accelerate_dragon)
+start()