On 8/3/22 06:36, Sean Cole via use-livecode wrote:
Hi all,
I've been thinking about the command 'dispatch'. Is there any
advantage/disadvantage in using it over just calling your handler?

If you can invoke a command/function directly then for the most part there's no real advantage in using dispatch.

I never use send anymore unless I need send a message in time.
I do use dispatch extensively, mostly for two reasons.

One, if I'm calling a handler in a different object that is outside the normal message path then I'll dispatch the handler to that object rather than using send. One caveat: note that the dispatch command returns a three-state value: "handled", "unhandled", and "passed". So on checking the return value I use "if it it not unhandled then...". The advantage is that there's no runtime error if the command isn't caught, at the slight disadvantage of having to check whether it was handled.

The second case where I use dispatch is as a form of publish/subscribe: dispatching a command without a receiver object sends the command along the message path where it can be handled/passed by any object along the way. Or not. Mostly in this paradigm I don't need or want to check the return value because it's irrelevant to the sender whether or not the message was handled.

The dispatch command can also be useful for feature management. Dispatch a command down the message path, and if the given feature is enabled then the command will be handled. If not then there's no downside to calling the feature because it won't cause a runtime error.

 Mark Wieder

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