CancellablesManager.swift

public class CancellablesManager {
    private let lock = NSLock()
    
    public typealias Storage = Set<AnyCancellable>
    private var cancellables: Storage = []
    
    func store(_ element: AnyCancellable?, _ precondition: Bool = true) {
        lock.execute {
            guard precondition, let element = element else { return }
            cancellables.insert(element)
            print("i", cancellables.map { $0.hashValue })
        }
    }
    
    func release(_ element: AnyCancellable?, completion: () -> Void = {}) {
        lock.execute {
            guard let element = element else { return }
            cancellables.remove(element)
            completion()
        }
    }
    
}

extension AnyCancellable {
    func store(in manager: CancellablesManager) {
        manager.store(self)
    }
}

extension Publisher {
    
    @discardableResult
    public func sink(using manager: CancellablesManager,
                     onCompletion: @escaping (Subscribers.Completion<Self.Failure>) -> Void,
                     onSuccess: @escaping (Self.Output) -> Void) -> AnyCancellable {
        var cancellable: AnyCancellable?
        var didComplete = false
        
        let release: () -> Void = { [weak manager] in
            manager?.release(cancellable) { didComplete = true }
        }
        
        cancellable = handleEvents(receiveCancel: release)
            .sink(
                receiveCompletion: { completion in
                    release()
                    onCompletion(completion)
                },
                receiveValue: { value in
                    release()
                    onSuccess(value)
            })
        
        manager.store(cancellable, !didComplete)
        
        return cancellable!
    }
    
}

Example.swift

typealias Reducer<State, Action> = (inout State, Action) -> Void

final class Store<State, Action>: ObservableObject {
    typealias Effect = AnyPublisher<Action, Never>
    
    @Published private(set) var state: State
    
    private let lock: NSLock = .init()
    private let reducer: Reducer<State, Action>
    private let cancellablesManager = CancellablesManager()
    
    init(state: State, reducer: @escaping Reducer<State, Action>) {
        self.state = state
        self.reducer = reducer
    }
    
    func send(_ effect: Effect) {
        effect
            .receive(on: RunLoop.main)
            .sink(using: cancellablesManager,
                  onCompletion: executeNothing(),
                  onSuccess: send)
    }
    
    func send(_ action: Action) {
        lock.execute {
            print(log(state, action))
            reducer(&state, action)
        }
    }
    
    func log(_ state: State, _ action: Action) -> String {
        let logId = UUID()
        return
            "#startlog {\(logId.uuidString)}:\n" +
                ">   Date   : \(Date())\n" +
                ">   State  : \(state)\n"  +
                ">   Action : \(action)\n" +
            "#endlog   {\(logId.uuidString)}."
    }
}

extension Store {
    func binding<Value>(
        for keyPath: KeyPath<State, Value>,
        _ action: @escaping (Value) -> Action
    ) -> Binding<Value> {
        .init(get: { self.state[keyPath: keyPath] }, set: { self.send(action($0)) })
    }
}

NSLock+Extension.swift

extension NSLock {
    
    func store<T>(_ value: T, in object: inout T) {
        mutate(&object, with: { $0 = value })
    }
    
    func mutate<T: AnyObject>(_ object: T, with closure: (T) -> Void) {
        execute { closure(object) }
    }
    
    func mutate<T>(_ object: inout T, with closure: (inout T) -> Void) {
        execute { closure(&object) }
    }
    
    @discardableResult
    func execute<T>(code closure: () -> T) -> T {
        lock()
        defer { unlock() }
        return closure()
    }
    
}

It would be nice to have a readme/docs in Merge 🙂