Callbacks

Type Checking

Added in version 1.1.0.

oop-ext also provides type-checked variants, Callback0, Callback1, Callback2, etc, which explicitly declare the number of arguments and types of the parameters supported by the callback.

Example:

class Point:
    def __init__(self, x: float, y: float) -> None:
        self._x = x
        self._y = y
        self.on_changed = Callback2[float, float]()

    def update(self, x: float, y: float) -> None:
        self._x = x
        self._y = y
        self.on_changed(x, y)


def on_point_changed(x: float, y: float) -> None:
    print(f"point changed: ({x}, {y})")


p = Point(0.0, 0.0)
p.on_changed.Register(on_point_changed)
p.update(100.0, 2.5)

In the example above, both the calls self.on_changed and on_changed.Register are properly type checked for number of arguments and types.

The method specialized signatures are only seen by the type checker, so using one of the specialized variants should have nearly zero runtime cost (only the cost of an empty subclass).

Added in version 2.2.0.

PriorityCallback has the same support, with PriorityCallback0, PriorityCallback1, PriorityCallback2, etc.

Note

The separate callback classes are needed for now, but once we require Python 3.11 (pep-0646, we should be able to implement the generic variants into Callback and PriorityCallback themselves.