callbacks.rst

Callbacks

oop_ext.foundation.callback._callback

Type Checking

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).

Note

The separate callback classes are needed for now, but if/when pep-0646 lands, we should be able to implement the generic variants into Callback itself.