Matching message attributes with "on" decorator, without using CSS selectors.

[aaronrudkin]

I have a message class which has a property called mode, which is a string that contains a mode switch. I do this because a widget is going to be passing a wide variety of messages to the parent and I don't want to create a billion different message classes (though, I recognize that I could). My sense was that the on decorator's kwargs argument should allow the on decorator to dispatch matching on this property.

Thus the idea would be the parent app could have methods like the following:

@on(MyWidget.MessageClass, mode="select")
def select_the_thing(self, message: MyWidget.MessageClass):
   ...

@on(MyWidget.MessageClass, mode="deselect")
def deselect_the_thing(self, message: MyWidget.MessageClass):
   ...

The alternatives being, obviously, to have a single message catcher that dispatches with if-elif or a dispatch table inside the function, or else to have multiple message classes.

The reason this doesn't work is that the kwargs argument of the on dispatcher wants to parse the mode argument here as a css selector. Which makes sense if the object you're matching against is a widget, but less so if you think about the message as directly exposing the attributes you want to match on.

Any thoughts about an elegant way to do this? If the idea is that the on decorator is only going to match on selectors then I'll probably go back to using a dispatch table inside one message catching function.