Clean up from #61

- Refine docs and assert messages
- Apply swiftlint fixes
- Avoid possible retain cycle

Author: jessesquires

Sources/ObserverTrampoline.swift

@@ -13,32 +13,39 @@
 
 import Foundation
 
-/// Watches for changes to UserDefaults using old-school Key-Value Observing.
+/// 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.
+/// 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.
+/// 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
+    private let action: () -> 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 '.'")
+    init(userDefaults: UserDefaults, key: String, action: @escaping () -> Void) {
+        assert(!key.hasPrefix("@"), "Error: key name cannot begin with a '@' character and be observed via KVO.")
+        assert(!key.contains("."), "Error: key name cannot contain a '.' character anywhere and be observed via KVO.")
         self.userDefaults = userDefaults
         self.key = key
-        self.block = block
+        self.action = action
         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 {
+        self.userDefaults.removeObserver(self, forKeyPath: self.key, context: nil)
     }
 
-    deinit {
-        userDefaults.removeObserver(self, forKeyPath: key, context: nil)
+    // swiftlint:disable:next block_based_kvo
+    override func observeValue(
+        forKeyPath keyPath: String?,
+        of object: Any?,
+        // swiftlint:disable:next discouraged_optional_collection
+        change: [NSKeyValueChangeKey: Any]?,
+        context: UnsafeMutableRawPointer?) {
+            self.action()
     }
 }

Sources/WrappedDefault.swift

@@ -55,7 +55,7 @@ public struct WrappedDefault<T: UserDefaultsSerializable> {
         // and uses force unwrap
         self._publisher = CurrentValueSubject<T, Never>(userDefaults.fetch(keyName))
 
-        self._observer = ObserverTrampoline(userDefaults: userDefaults, key: keyName) { [_publisher] in
+        self._observer = ObserverTrampoline(userDefaults: userDefaults, key: keyName) { [unowned _publisher] in
             _publisher.send(userDefaults.fetch(keyName))
         }
     }

Sources/WrappedDefaultOptional.swift

@@ -52,7 +52,7 @@ 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
+        self._observer = ObserverTrampoline(userDefaults: userDefaults, key: keyName) { [unowned _publisher] in
             _publisher.send(userDefaults.fetchOptional(keyName))
         }
     }