The last piece: an effect is a side effect that runs immediately and then re-runs whenever any state it depends on changes, logging, rendering, syncing to storage. It is the bridge from reactive values back out to the real world, and it must be disposable so it can stop.
create_effect(fn, sources): run fn once now, subscribe it to re-run on every change of each source in sources, and return a dispose function that cancels all of those subscriptionsclass Subject:
def __init__(self):
self._observers = []
def subscribe(self, observer):
self._observers.append(observer)
def unsubscribe():
if observer in self._observers:
self._observers.remove(observer)
return unsubscribe
def notify(self, *args):
for observer in self._observers:
observer(*args)
class Observable:
def __init__(self, value=None):
self._value = value
self._subject = Subject()
def get(self):
return self._value
def subscribe(self, observer):
return self._subject.subscribe(observer)
def set(self, value):
if value == self._value:
return
self._value = value
self._subject.notify(value)
def create_effect(fn, sources):
"""Run fn now and on every change of any source; return a dispose function."""
# TODO: invoke fn once right away so the effect reflects the current state, then
# register on every source in sources an observer that ignores whatever value
# it is handed and simply re-runs fn, collecting the unsubscribe handle each
# subscription returns. Hand back a function that fires all of those handles.
pass
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The last piece: an effect is a side effect that runs immediately and then re-runs whenever any state it depends on changes, logging, rendering, syncing to storage. It is the bridge from reactive values back out to the real world, and it must be disposable so it can stop.
create_effect(fn, sources): run fn once now, subscribe it to re-run on every change of each source in sources, and return a dispose function that cancels all of those subscriptionsPress Run Tests or ⌘↩ to check your solution.