Combine: withLatestFrom, 04

code.swift

import Combine

extension Publishers {
    public struct WithLatestFrom<Upstream: Publisher, Other: Publisher>:
        Publisher where Upstream.Failure == Other.Failure
    {
        // MARK: - Types

        public typealias Output = (Upstream.Output, Other.Output)
        public typealias Failure = Upstream.Failure

        // MARK: - Properties

        private let upstream: Upstream
        private let other: Other

        // MARK: - Initialization

        init(upstream: Upstream, other: Other) {
            self.upstream = upstream
            self.other = other
        }

        // MARK: - Publisher Lifecycle

        public func receive<S: Subscriber>(subscriber: S)
            where S.Failure == Failure, S.Input == Output
        {
            let merged = mergedStream(upstream, other)
            let result = resultStream(from: merged)
            result.subscribe(subscriber)
        }
    }
}

// MARK: - Helpers
private extension Publishers.WithLatestFrom {
    // MARK: - Types

    enum MergedElement {
        case upstream1(Upstream.Output)
        case upstream2(Other.Output)
    }

    typealias ScanResult =
        (value1: Upstream.Output?,
         value2: Other.Output?, shouldEmit: Bool)

    // MARK: - Pipelines

    func mergedStream(_ upstream1: Upstream, _ upstream2: Other)
        -> AnyPublisher<MergedElement, Failure>
    {
        let mergedElementUpstream1 = upstream1
            .map { MergedElement.upstream1($0) }
        let mergedElementUpstream2 = upstream2
            .map { MergedElement.upstream2($0) }
        return mergedElementUpstream1
            .merge(with: mergedElementUpstream2)
            .eraseToAnyPublisher()
    }

    func resultStream(
        from mergedStream: AnyPublisher<MergedElement, Failure>
    ) -> AnyPublisher<Output, Failure>
    {
        mergedStream
            .scan(nil) {
                (prevResult: ScanResult?,
                mergedElement: MergedElement) -> ScanResult? in

                var newValue1: Upstream.Output?
                var newValue2: Other.Output?
                let shouldEmit: Bool

                switch mergedElement {
                case .upstream1(let v):
                    newValue1 = v
                    shouldEmit = prevResult?.value2 != nil
                case .upstream2(let v):
                    newValue2 = v
                    shouldEmit = false
                }

                return ScanResult(value1: newValue1 ?? prevResult?.value1,
                                  value2: newValue2 ?? prevResult?.value2,
                                  shouldEmit: shouldEmit)
        }
        .compactMap { $0 }
        .filter { $0.shouldEmit }
        .map { Output($0.value1!, $0.value2!) }
        .eraseToAnyPublisher()
    }
}

extension Publisher {
    func withLatestFrom<Other: Publisher>(_ other: Other)
        -> Publishers.WithLatestFrom<Self, Other>
    {
        return .init(upstream: self, other: other)
    }
}

Hi Seyoung, Feel free to use any of my code at your discretion and responsibility. Regards, Serhiy

…

On Jul 21, 2024, at 11:42 PM, seyoung.hyun ***@***.***> wrote: @seyoung-hyun commented on this gist. Thanks your code :) Can I use your code in my commercial app? Please let me know how I can use the code for commercial distribution. — Reply to this email directly, view it on GitHub <https://gist.github.com/serhiybutz/59d1c674c53f8a23d2ac773490410940#gistcomment-5128753> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFOAOKPLNO5ZGG4WOIIG3N3ZNR5QZBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDUOJ2WLJDOMFWWLO3UNBZGKYLEL5YGC4TUNFRWS4DBNZ2F6YLDORUXM2LUPGBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVEYTANBUG42TKNJZU52HE2LHM5SXFJTDOJSWC5DF>. You are receiving this email because you authored the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.