Encapsulates the steps necessary to tear down some unit of work, typically an asynchronous operation like a network task.

Disposable.swift

import Foundation

/// `Disposable` encapsulates the steps necessary to tear down some unit of work, typically an asynchronous operation
/// like a network task.
public protocol Disposable {
    /// Disposes the object. This may be invoked multiple times, but only performs its side-effects once.
    func dispose()
}

extension URLSessionTask: Disposable {
    func dispose() {
        cancel()
    }
}

extension Operation: Disposable {
    func dispose() {
        cancel()
    }
}

/// `AnyDisposable` takes a block and invokes it once on dispose. This class guarantees thread safety.
public final class AnyDisposable: Disposable {
    public typealias Action = () -> ()
    
    // the disposable is optional because we nil it out after it's invoked to prevent multiple invocations.
    private var disposable: Action?
    private let queue = DispatchQueue(label: "disposable")
    
    public init(_ disposable: @escaping Action) {
        self.disposable = disposable
    }
    
    public func dispose() {
        self.queue.async {
            if let disposable = self.disposable {
                disposable()
            }
            
            self.disposable = nil
        }
    }
}