[#140] Removed containsValue(forKey:) from Feature-Flag Stores (#141)

* Removed the `containsValue(forKey:` method from protocols for feature-flag stores to prevent conflicts between this method and `value(forKey:)`
* Introduced `FeatureFlagStoreError` which contains two predefined error cases: `valueNotFound` and `typeMismatch`; `valueNotFound` is especially important as it determines the behavior of `FeatureFlagResolver`
* Updated the `value(forKey:)` methods’ return type to `Result<Value, FeatureFlagStoreError>`
* Updated `FeatureFlagResolver`
* Updated the built-in stores
* Removed `CommonFeatureFlagStoreError`
* Updated tests

Sources/YMFF/FeatureFlagResolver/FeatureFlagResolver.swift

@@ -164,11 +164,16 @@ extension FeatureFlagResolver {
         }
 
         for store in matchingStores {
-            if await store.containsValue(forKey: key) {
-                do {
-                    let value: Value = try await store.value(forKey: key)
-                    return value
-                } catch {
+            switch await store.value(forKey: key) as Result<Value, _> {
+            case .success(let value):
+                return value
+            case .failure(let error):
+                switch error {
+                case .valueNotFound:
+                    continue
+                case .typeMismatch:
+                    throw Error.storeError(error)
+                case .otherError(let error):
                     throw Error.storeError(error)
                 }
             }
@@ -184,11 +189,16 @@ extension FeatureFlagResolver {
         }
 
         for store in matchingStores {
-            if store.containsValueSync(forKey: key) {
-                do {
-                    let value: Value = try store.valueSync(forKey: key)
-                    return value
-                } catch {
+            switch store.valueSync(forKey: key) as Result<Value, _> {
+            case .success(let value):
+                return value
+            case .failure(let error):
+                switch error {
+                case .valueNotFound:
+                    continue
+                case .typeMismatch:
+                    throw Error.storeError(error)
+                case .otherError(let error):
                     throw Error.storeError(error)
                 }
             }

Sources/YMFF/FeatureFlagResolver/Store/RuntimeOverridesStore.swift

@@ -27,14 +27,10 @@ final public class RuntimeOverridesStore {
 
 extension RuntimeOverridesStore: SynchronousMutableFeatureFlagStore {
 
-    public func containsValueSync(forKey key: String) -> Bool {
-        store[key] != nil
-    }
-
-    public func valueSync<Value>(forKey key: String) throws -> Value {
-        guard let anyValue = store[key] else { throw CommonFeatureFlagStoreError.valueNotFound(key: key) }
-        guard let value = anyValue as? Value else { throw CommonFeatureFlagStoreError.typeMismatch }
-        return value
+    public func valueSync<Value>(forKey key: String) -> Result<Value, FeatureFlagStoreError> {
+        guard let anyValue = store[key] else { return .failure(.valueNotFound) }
+        guard let value = anyValue as? Value else { return .failure(.typeMismatch) }
+        return .success(value)
     }
 
     public func setValueSync<Value>(_ value: Value, forKey key: String) {

Sources/YMFF/FeatureFlagResolver/Store/TransparentFeatureFlagStore.swift

@@ -19,14 +19,10 @@ public typealias TransparentFeatureFlagStore = [String: Any]
 
 extension TransparentFeatureFlagStore: SynchronousFeatureFlagStore, FeatureFlagStore {
 
-    public func containsValueSync(forKey key: String) -> Bool {
-        self[key] != nil
-    }
-
-    public func valueSync<V>(forKey key: String) throws -> V {
-        guard let anyValue = self[key] else { throw CommonFeatureFlagStoreError.valueNotFound(key: key) }
-        guard let value = anyValue as? V else { throw CommonFeatureFlagStoreError.typeMismatch }
-        return value
+    public func valueSync<V>(forKey key: String) -> Result<V, FeatureFlagStoreError> {
+        guard let anyValue = self[key] else { return .failure(.valueNotFound) }
+        guard let value = anyValue as? V else { return .failure(.typeMismatch) }
+        return .success(value)
     }
 
 }

Sources/YMFF/FeatureFlagResolver/Store/UserDefaultsStore.swift

@@ -34,16 +34,10 @@ final public class UserDefaultsStore {
 
 extension UserDefaultsStore: SynchronousMutableFeatureFlagStore {
 
-    public func containsValueSync(forKey key: String) -> Bool {
-        userDefaults.object(forKey: key) != nil
-    }
-
-    public func valueSync<Value>(forKey key: String) throws -> Value {
-        guard let anyValue = userDefaults.object(forKey: key) else {
-            throw CommonFeatureFlagStoreError.valueNotFound(key: key)
-        }
-        guard let value = anyValue as? Value else { throw CommonFeatureFlagStoreError.typeMismatch }
-        return value
+    public func valueSync<Value>(forKey key: String) -> Result<Value, FeatureFlagStoreError> {
+        guard let anyValue = userDefaults.object(forKey: key) else { return .failure(.valueNotFound) }
+        guard let value = anyValue as? Value else { return .failure(.typeMismatch) }
+        return .success(value)
     }
 
     public func setValueSync<Value>(_ value: Value, forKey key: String) {

Sources/YMFFProtocols/FeatureFlagResolver/Store/FeatureFlagStore.swift

@@ -9,14 +9,9 @@
 /// An object that stores feature flag values, and provides them at the resolver's request.
 public protocol FeatureFlagStore {
 
-    /// Indicates whether the store contains a value that corresponds to the key.
-    ///
-    /// - Parameter key: *Required.* The key.
-    func containsValue(forKey key: String) async -> Bool
-
     /// Retrieves a feature flag value by its key.
     ///
     /// - Parameter key: *Required.* The key that points to a feature flag value in the store.
-    func value<Value>(forKey key: String) async throws -> Value
+    func value<Value>(forKey key: String) async -> Result<Value, FeatureFlagStoreError>
 
 }

Sources/YMFFProtocols/FeatureFlagResolver/Store/FeatureFlagStoreError.swift

@@ -0,0 +1,13 @@
+//
+//  FeatureFlagStore.swift
+//  YMFFProtocols
+//
+//  Created by Yakov Manshin on 5/11/24.
+//  Copyright © 2024 Yakov Manshin. See the LICENSE file for license info.
+//
+
+public enum FeatureFlagStoreError: Error {
+    case valueNotFound
+    case typeMismatch
+    case otherError(any Error)
+}

Sources/YMFFProtocols/FeatureFlagResolver/Store/SynchronousFeatureFlagStore.swift

@@ -8,28 +8,19 @@
 
 public protocol SynchronousFeatureFlagStore: FeatureFlagStore {
 
-    /// Indicates whether the store contains a value that corresponds to the key.
-    ///
-    /// - Parameter key: *Required.* The key.
-    func containsValueSync(forKey key: String) -> Bool
-
     /// Retrieves a feature flag value by its key.
     ///
     /// - Parameter key: *Required.* The key that points to a feature flag value in the store.
-    func valueSync<Value>(forKey key: String) throws -> Value
+    func valueSync<Value>(forKey key: String) -> Result<Value, FeatureFlagStoreError>
 
 }
 
 // MARK: - Async Requirements
 
 extension SynchronousFeatureFlagStore {
 
-    public func containsValue(forKey key: String) async -> Bool {
-        containsValueSync(forKey: key)
-    }
-
-    public func value<Value>(forKey key: String) async throws -> Value {
-        try valueSync(forKey: key)
+    public func value<Value>(forKey key: String) async -> Result<Value, FeatureFlagStoreError> {
+        valueSync(forKey: key)
     }
 
 }