Useful extensions for Combine Publisher

Publisher.swift

extension Publisher where Failure == Never {
    
    public func sink<Root>(to handler: @escaping (Root) -> (Output) -> Void, on root: Root) -> AnyCancellable where Root: AnyObject {
        sink{ [weak root] value in
            guard let root = root else { return }
            handler(root)(value)
        }
    }
    
    public func sink<Root>(to handler: @escaping (Root) -> () -> Void, on root: Root) -> AnyCancellable where Root: AnyObject {
        sink{ [weak root] _ in
            guard let root = root else { return }
            handler(root)()
        }
    }
}

extension Publisher {
    
    public func eraseToAnyError() -> Publishers.MapError<Self, Error> {
        mapError { $0 as Error }
    }
    
    public func `catch`(_ handler: @escaping (Failure) -> Output) -> Publishers.Catch<Self, Just<Output>> {
        `catch`{ error in Just(handler(error)) }
    }
    
    public func flatMap<P>(
        maxPublishers: Subscribers.Demand = .unlimited,
        _ transform: @escaping (Output) -> P
    ) -> Publishers.FlatMap<Publishers.MapError<P, Error>, Publishers.MapError<Self, Error>> where P: Publisher {
        eraseToAnyError().flatMap { output in
            transform(output).eraseToAnyError()
        }
    }
}