Case Paths + Key Paths = Optional Paths

Package.swift

@@ -20,7 +20,7 @@ let package = Package(
   dependencies: [
     .package(url: "https://github.com/swiftlang/swift-syntax", "509.0.0"..<"601.0.0-prerelease"),
     .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.2.2"),
-    .package(url: "https://github.com/pointfreeco/swift-macro-testing", from: "0.2.0"),
+    .package(url: "https://github.com/pointfreeco/swift-macro-testing", from: "0.5.2"),
   ],
   targets: [
     .target(

Package@swift-6.0.swift

@@ -19,8 +19,8 @@ let package = Package(
   ],
   dependencies: [
     .package(url: "https://github.com/swiftlang/swift-syntax", "509.0.0"..<"601.0.0-prerelease"),
+    .package(url: "https://github.com/pointfreeco/swift-macro-testing", from: "0.5.2"),
     .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.2.2"),
-    .package(url: "https://github.com/pointfreeco/swift-macro-testing", from: "0.2.0"),
   ],
   targets: [
     .target(
@@ -50,7 +50,7 @@ let package = Package(
       ]
     ),
   ],
-  swiftLanguageVersions: [.v6]
+  swiftLanguageModes: [.v6]
 )
 
 #if !os(Windows)

Sources/CasePaths/AnyOptionalPath.swift

@@ -0,0 +1,67 @@
+import Foundation
+
+/// A type-erased optional path that supports extracting an optional value from a root, and
+/// non-optionally updating a value when present.
+///
+/// This type defines key path-like semantics for optional-chaining.
+public struct AnyOptionalPath<Root, Value>: Sendable {
+  private let _get: @Sendable (Root) -> Value?
+  private let _set: @Sendable (inout Root, Value) -> Void
+
+  /// Creates a type-erased optional path from a pair of functions.
+  ///
+  /// - Parameters:
+  ///   - get: A function that can optionally fail in extracting a value from a root.
+  ///   - set: A function that always succeeds in updating a value in a root when present.
+  public init(
+    get: @escaping @Sendable (Root) -> Value?,
+    set: @escaping @Sendable (inout Root, Value) -> Void
+  ) {
+    self._get = get
+    self._set = set
+  }
+
+  /// Creates a type-erased optional path from a type-erased case path.
+  ///
+  /// - Parameters:
+  ///   - get: A function that can optionally fail in extracting a value from a root.
+  ///   - set: A function that always succeeds in updating a value in a root when present.
+  public init(_ casePath: AnyCasePath<Root, Value>) {
+    self.init(get: casePath.extract) { $0 = casePath.embed($1) }
+  }
+
+  /// Attempts to extract a value from a root.
+  ///
+  /// - Parameter root: A root to extract from.
+  /// - Returns: A value if it can be extracted from the given root, otherwise `nil`.
+  public func extract(from root: Root) -> Value? {
+    self._get(root)
+  }
+
+  /// Returns a root by embedding a value.
+  ///
+  /// - Parameters:
+  ///   - root: A root to modify.
+  ///   - value: A value to update in the root when an existing value is present.
+  public func set(into root: inout Root, _ value: Value) {
+    self._set(&root, value)
+  }
+}
+
+extension AnyOptionalPath where Root == Value {
+  /// The identity optional path.
+  ///
+  /// An optional path that:
+  ///
+  ///   * Given a value to extract, returns the given value.
+  ///   * Given a value to update, replaces the given value.
+  public init() where Root == Value {
+    self.init(get: { $0 }, set: { $0 = $1 })
+  }
+}
+
+extension AnyOptionalPath: CustomDebugStringConvertible {
+  public var debugDescription: String {
+    "AnyOptionalPath<\(typeName(Root.self)), \(typeName(Value.self))>"
+  }
+}

Sources/CasePaths/CasePathIterable.swift

@@ -14,4 +14,4 @@
 /// Array(Field.allCasePaths)  // [\.title, \.body, \.isLive]
 /// ```
 public protocol CasePathIterable: CasePathable
-where AllCasePaths: Sequence, AllCasePaths.Element == PartialCaseKeyPath<Self> {}
+where AllCasePaths: Sequence, AllCasePaths.Element == PartialOptionalKeyPath<Self> {}

Sources/CasePaths/CasePathReflectable.swift

@@ -23,5 +23,5 @@ public protocol CasePathReflectable<Root> {
   ///
   /// - Parameter root: An root value.
   /// - Returns: A case path to the root value.
-  subscript(root: Root) -> PartialCaseKeyPath<Root> { get }
+  subscript(root: Root) -> PartialOptionalKeyPath<Root> { get }
 }