pyDynECS component manager mutators

[mason-bially]

Need mutator classes for pyDynECS. These are callable()s which take an IComponentManager class and mutate it's functionality. Below are some mutators we need.

A common pattern for implementing this is to use a function with an anonymous class definition. Mutator order will be important:

_cache_exampleMutator = {}
def ExampleMutator(cls):
    if not (cls in _cache_exampleMutator):
        class MutatedExample(cls):
            ...
        # Better names for inspection:
        MutatedExample.__qualname__ = "MutatedExample<{}>".format(cls.__qualname__)
        _cache_exampleMutator[cls] = MutatedExample
    return _cache_exampleMutator[cls]

# Usage:
component_manager = ExampleMutator(BasicComponentManager)()
# or
class NewComponentManagerType(ExampleMutator(BasicComponentManager)):
    ...

Mutators:

• Observable(cls, event_type=pyext.Event): Adds events for mutating functions (add, set, del) with the naming scene on_*. Where on_add is triggered before on_set for entities that currently have no component. The events have the following signature (manager, entity, overriding=None) where overriding is only for on_set (on_del is called before the component is actually removed).
• Immutable(cls): Removes del, forces set to only be called once (exception otherwise).
• Typed/Coering: Refactor the existing non-basic component manager types to be mutators. They don't do enough different to be fully fledged different classes. Also move the coercing/typed function to the class, instead of the constructor.

[mason-bially]

Handeled with mixins instead.