TIL about Publishers.MergeMany.init

13 Dec 2019 ⇐ Notes archive

(This is an entry in my technical notebook. There will likely be typos, mistakes, or wider logical leaps — the intent here is to “let others look over my shoulder while I figure things out.”)

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A few weeks back, Jordan Morgan nerd sniped me¹ into writing a Combine analog to RxSwift’s ObservableType.merge(sources:)—an operator that can merge arbitrarily many observable sequences.

Here’s a rough, not-tested-in-production sketch (if you know a way to ease the eraseToAnyPublisher dance, let me know):

And in writing this entry, I decided to check and make sure I wasn’t missing something. After all, it’s odd (pun intended) that the merging operators on Publisher stop at arity seven.

Then, I noticed the Publishers.MergeMany return value on the first and, below the (hopefully temporary) “No overview available” note on its documentation, there’s a variadic initializer!

So, there you have it. TIL merging a sequence of publishers goes by the name of Publishers.MergeMany.init(_:).

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