Custom Operator wiki article a little out of sync with practice

[davidmoten]

The wiki article Implementing Your Own Operators mentions the following:

Your sequence operator should check its Subscriber's isUnsubscribed( ) status before it emits any item to (or sends any notification to) the Subscriber. Do not waste time generating items that no Subscriber is interested in seeing.

This appears to be a pretty conservative approach given that the base operators of RxJava don't follow this uniformly. For example OperatorDistinct, OperatorMap.

Perhaps the article could add that these checks are not essential if for instance better performance was desired and benchmarks indicated that there was a significant advantage to not making the isUnsubscribed() check.

My rule of thumb at the moment is that when I receive a notification to the parent subscriber I check isUnsubscribed() only when that single notification corresponds to multiple notifications to the child subscriber. Does this seem fair?

So I suspect the article could do with a bit of enhancement in this regard. Any more ideas on what to say?

[davidmoten]

Another useful addition to the wiki article would be a section Testing your Operator that lists the standard tests being discussed in #1962 (like!)

[akarnokd]

See https://github.com/ReactiveX/RxJava/wiki/Implementing-custom-operators-(draft)

[akarnokd]

Closing this for now in favor of https://github.com/ReactiveX/RxJava/wiki/Implementing-custom-operators-(draft) . Let me know if something is missing or not explained well.