Added DeallocToken

Sources/Entwine/Utilities/DeallocToken.swift

@@ -0,0 +1,41 @@
+//
+//  Entwine
+//  https://github.com/tcldr/Entwine
+//
+//  Copyright © 2019 Tristan Celder. All rights reserved.
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in
+//  all copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+//  THE SOFTWARE.
+
+import Combine
+
+/// An object that notifies of its deallocation via a publisher sequence
+public final class DeallocToken {
+
+    private let subject = PassthroughSubject<(), Never>()
+
+    /// A publisher that, upon deallocation of the token, publishes a single element and then immediately completes.
+    public var publisher: AnyPublisher<(), Never> { subject.eraseToAnyPublisher() }
+
+    public init() {}
+
+    deinit {
+        subject.send()
+        subject.send(completion: .finished)
+    }
+}