Untitled

import Combine

final class AnySubject<Output, Failure: Error>: Subject {
    
    public let base: Any
    
    let _baseAsAnyPublisher: AnyPublisher<Output, Failure>
    let _send: (Output) -> Void
    let _sendCompletion: (Subscribers.Completion<Failure>) -> Void
    let _sendSubscription: (Subscription) -> Void
    
    public init<S: Subject>(_ subject: S) where S.Output == Output, S.Failure == Failure {
        base = subject
        
        _baseAsAnyPublisher = subject.eraseToAnyPublisher()
        _send = subject.send
        _sendCompletion = subject.send
        _sendSubscription = subject.send
    }
    
    public func receive<S: Subscriber>(subscriber: S) where Failure == S.Failure, Output == S.Input {
        _baseAsAnyPublisher.receive(subscriber: subscriber)
    }
    
    public func send(_ value: Output) {
        _send(value)
    }
    
    public func send(completion: Subscribers.Completion<Failure>) {
        _sendCompletion(completion)
    }
    
    public func send(subscription: Subscription) {
        _sendSubscription(subscription)
    }
}

extension Subject {
    
    func eraseToAnySubject() -> AnySubject<Output, Failure> {
        return AnySubject(self)
    }
    
}