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swiftreactive-programmingcombine

Is there a reactive function which executes and passes the original value?

I have a flow which transforms data, acts on it, transform it again, and acts on that. For example:

// Current code
Just(0)
    .map({ $0 + 1 })
    .map({ funcX($0); return $0 })
    .map({ $0 + 1 })
    .map({ funcY($0); return $0 })
    ...

I know reactive programming is about streams, but I would like to call funcX without needing to return the value. Is there a function which passes in the value and automatically passes along the value? Something like:

// Hypothetical
Just(0)
    .map({ $0 + 1 })
    .call({ funcX($0) })
    .map({ $0 + 1 })
    .call({ funcY($0) })
    ...

Note: The above swift needs more syntax to actually compile, just is an example.

Solution

  • No need for a custom operator, one already exists: handleEvents

    Just(0)
    .map({ $0 + 1 })
    .handleEvents(receiveOutput: { funcX($0) })
    .map({ $0 + 1 })
    .handleEvents(receiveOutput: { funcY($0) })
    ...

    The handleEvents operator can hook into any part of the publisher/subscriber lifecycle with it's optional parameters:

    • receiveSubscription

    • receiveRequest

    • receiveCancel

    • receiveOutput

    • receiveCompletion