Send on projectedValue publisher for any change (#61)

Previously, only when using the property wrapper's setter would the
projected publisher send a new value. This ignored changes from:

- Other instances of the property wrapper.
- Other libraries that persist to UserDefaults.
- Direct callers of UserDefaults.
- Other processes.

Now the publisher sends the new value no matter where the change occurs.

Assert observe key path will actually send changes. UserDefaults will silently ignore observation requests for keys that start with `@`. Keys that contain a `.` will be treated as key paths and cannot be directly observed using KVO.

Author: nolanw

CHANGELOG.md

@@ -7,6 +7,22 @@ NEXT
 
 - TBA
 
+4.0.0
+-----
+
+### New
+
+- The publisher projected by the property wrapper now sends values when user defaults changes from anywhere. Previously, only when using the property wrapper's setter would the projected publisher send a new value. ([#61](https://github.com/jessesquires/Foil/pull/61), [@nolanw](https://github.com/nolanw))
+
+### Breaking
+
+- Due to [#61](https://github.com/jessesquires/Foil/pull/61) (see above), there are some (potentially) breaking changes with key names. If any of your keys are named like the following examples and you need to observe changes, you will need to migrate your key names.
+    - Key names starting with an `@` character **do not** notify observers on updates.
+        - Example: `@my-key-name`
+    - Key names containing a `.` character _anywhere_ in the name **do not** notify observers on updates. (This is a side-effect of `KeyPaths` which include periods.)
+        - Example: `com.myApp.my-key-name`
+
+
 3.0.0
 -----
 

Foil.xcodeproj/project.pbxproj

@@ -17,6 +17,7 @@
 		0BF54A9D25BF58B1008484F8 /* UserDefaults+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0BF54A9C25BF58B1008484F8 /* UserDefaults+Extensions.swift */; };
 		0BF5FD9025C14A7D0003B078 /* WrappedDefault.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0BF5FD8F25C14A7D0003B078 /* WrappedDefault.swift */; };
 		0BF5FD9625C14A960003B078 /* UserDefaultsSerializable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0BF5FD9525C14A960003B078 /* UserDefaultsSerializable.swift */; };
+		1CC00F2428DAB1FC00EC2C63 /* ObserverTrampoline.swift in Sources */ = {isa = PBXBuildFile; fileRef = 1CC00F2328DAB1FC00EC2C63 /* ObserverTrampoline.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -41,6 +42,7 @@
 		0BF54A9C25BF58B1008484F8 /* UserDefaults+Extensions.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UserDefaults+Extensions.swift"; sourceTree = "<group>"; };
 		0BF5FD8F25C14A7D0003B078 /* WrappedDefault.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WrappedDefault.swift; sourceTree = "<group>"; };
 		0BF5FD9525C14A960003B078 /* UserDefaultsSerializable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UserDefaultsSerializable.swift; sourceTree = "<group>"; };
+		1CC00F2328DAB1FC00EC2C63 /* ObserverTrampoline.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ObserverTrampoline.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -83,6 +85,7 @@
 		0BF54A8225BF589E008484F8 /* Sources */ = {
 			isa = PBXGroup;
 			children = (
+				1CC00F2328DAB1FC00EC2C63 /* ObserverTrampoline.swift */,
 				0BF54A9C25BF58B1008484F8 /* UserDefaults+Extensions.swift */,
 				0BF5FD9525C14A960003B078 /* UserDefaultsSerializable.swift */,
 				0BF5FD8F25C14A7D0003B078 /* WrappedDefault.swift */,
@@ -236,6 +239,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				0BF5FD9625C14A960003B078 /* UserDefaultsSerializable.swift in Sources */,
+				1CC00F2428DAB1FC00EC2C63 /* ObserverTrampoline.swift in Sources */,
 				0BEEA2B22603F8390035387F /* WrappedDefaultOptional.swift in Sources */,
 				0BF5FD9025C14A7D0003B078 /* WrappedDefault.swift in Sources */,
 				0BF54A9D25BF58B1008484F8 /* UserDefaults+Extensions.swift in Sources */,

Sources/ObserverTrampoline.swift

@@ -0,0 +1,44 @@
+//
+//  Created by Jesse Squires
+//  https://www.jessesquires.com
+//
+//  Documentation
+//  https://jessesquires.github.io/Foil
+//
+//  GitHub
+//  https://github.com/jessesquires/Foil
+//
+//  Copyright © 2021-present Jesse Squires
+//
+
+import Foundation
+
+/// Watches for changes to UserDefaults using old-school Key-Value Observing.
+///
+/// KVO allows us to be notified of changes from anywhere (including other processes), not just via the property wrapper's setter.
+///
+/// We can't use Swift's block-based KVO because that requires a KeyPath, which we cannot create from a String.
+final class ObserverTrampoline: NSObject {
+    private let userDefaults: UserDefaults
+    private let key: String
+    private let block: () -> Void
+
+    init(userDefaults: UserDefaults, key: String, block: @escaping () -> Void) {
+        assert(!key.hasPrefix("@"), "Cannot observe a user default key starting with '@'")
+        assert(!key.contains("."), "Cannot observe a user default key containing '.'")
+        self.userDefaults = userDefaults
+        self.key = key
+        self.block = block
+        super.init()
+
+        userDefaults.addObserver(self, forKeyPath: key, context: nil)
+    }
+
+    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
+        block()
+    }
+
+    deinit {
+        userDefaults.removeObserver(self, forKeyPath: key, context: nil)
+    }
+}

Sources/WrappedDefault.swift

@@ -20,6 +20,7 @@ import Foundation
 public struct WrappedDefault<T: UserDefaultsSerializable> {
     private let _userDefaults: UserDefaults
     private let _publisher: CurrentValueSubject<T, Never>
+    private let _observer: ObserverTrampoline
 
     /// The key for the value in `UserDefaults`.
     public let key: String
@@ -31,7 +32,6 @@ public struct WrappedDefault<T: UserDefaultsSerializable> {
         }
         set {
             self._userDefaults.save(newValue, for: self.key)
-            self._publisher.send(newValue)
         }
     }
 
@@ -54,5 +54,9 @@ public struct WrappedDefault<T: UserDefaultsSerializable> {
         // because `fetch` assumes that `registerDefault` has been called before
         // and uses force unwrap
         self._publisher = CurrentValueSubject<T, Never>(userDefaults.fetch(keyName))
+
+        self._observer = ObserverTrampoline(userDefaults: userDefaults, key: keyName) { [_publisher] in
+            _publisher.send(userDefaults.fetch(keyName))
+        }
     }
 }

Sources/WrappedDefaultOptional.swift

@@ -20,6 +20,7 @@ import Foundation
 public struct WrappedDefaultOptional<T: UserDefaultsSerializable> {
     private let _userDefaults: UserDefaults
     private let _publisher: CurrentValueSubject<T?, Never>
+    private let _observer: ObserverTrampoline
 
     /// The key for the value in `UserDefaults`.
     public let key: String
@@ -32,10 +33,8 @@ public struct WrappedDefaultOptional<T: UserDefaultsSerializable> {
         set {
             if let newValue {
                 self._userDefaults.save(newValue, for: self.key)
-                self._publisher.send(newValue)
             } else {
                 self._userDefaults.delete(for: self.key)
-                self._publisher.send(nil)
             }
         }
     }
@@ -53,5 +52,8 @@ public struct WrappedDefaultOptional<T: UserDefaultsSerializable> {
         self.key = keyName
         self._userDefaults = userDefaults
         self._publisher = CurrentValueSubject<T?, Never>(userDefaults.fetchOptional(keyName))
+        self._observer = ObserverTrampoline(userDefaults: userDefaults, key: keyName) { [_publisher] in
+            _publisher.send(userDefaults.fetchOptional(keyName))
+        }
     }
 }

Tests/ObservationTests.swift

@@ -11,6 +11,7 @@
 //  Copyright © 2021-present Jesse Squires
 //
 
+@testable import Foil
 import Combine
 import XCTest
 
@@ -53,6 +54,27 @@ final class ObservationTests: XCTestCase {
         XCTAssertEqual(self.settings.average, publishedValue)
     }
 
+    func test_Integration_ProjectedValue_ExternalChange() {
+        let expectation = self.expectation(description: #function)
+        let expectedValue = 1_000.0
+        var publishedValue: Double?
+
+        self.settings.$average
+            .sink { newValue in
+                publishedValue = newValue
+
+                if newValue == expectedValue {
+                    expectation.fulfill()
+                }
+            }
+            .store(in: &self.cancellable)
+
+        type(of: self.settings).store.set(expectedValue, forKey: "average")
+        self.wait(for: [expectation], timeout: timeout)
+
+        XCTAssertEqual(self.settings.average, publishedValue)
+    }
+
     func test_Integration_Publisher() {
         let expectation = self.expectation(description: #function)
         var publishedValue: String?