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//
// TransformOperationObserver.swift
// MullvadVPN
//
// Created by pronebird on 06/07/2020.
// Copyright © 2020 Mullvad VPN AB. All rights reserved.
//
import Foundation
/// A private type erasing observer that type casts the input operation type to the expected
/// operation type before calling the wrapped observer
class TransformOperationObserver<S: OperationProtocol>: OperationObserver {
private let willExecute: (S) -> Void
private let willFinish: (S) -> Void
private let didFinish: (S) -> Void
init<T: OperationObserver>(_ observer: T) {
willExecute = Self.wrap(observer.operationWillExecute)
willFinish = Self.wrap(observer.operationWillFinish)
didFinish = Self.wrap(observer.operationDidFinish)
}
func operationWillExecute(_ operation: S) {
willExecute(operation)
}
func operationWillFinish(_ operation: S) {
willFinish(operation)
}
func operationDidFinish(_ operation: S) {
didFinish(operation)
}
private class func wrap<U>(_ body: @escaping (U) -> Void) -> (S) -> Void {
return { (operation: S) in
if let transformed = operation as? U {
body(transformed)
} else {
fatalError("\(Self.self) failed to cast \(S.self) to \(U.self)")
}
}
}
}
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