feat: Adding support for dynamic view controller types

WorkflowUI/Sources/ViewControllerDescription/ViewControllerDescription.swift

@@ -99,6 +99,56 @@ public struct ViewControllerDescription {
         }
     }
 
+    /// Constructs a view controller description by providing closures used to
+    /// build and update a specific view controller type. This initializer supports
+    /// implementations that cannot rely on static types.
+    ///
+    /// - Parameters:
+    ///   - performInitialUpdate: If an initial call to `update(viewController:)`
+    ///     will be performed when the view controller is created. Defaults to `true`.
+    ///
+    ///   - dynamicType: The type of view controller produced by this description.
+    ///     This type is used by `KindIdentifier` and its `checkViewControllerType`
+    ///     closure to inspect view controller types at runtime.
+    ///
+    ///   - environment: The `ViewEnvironment` that should be injected above the
+    ///     described view controller for ViewEnvironmentUI environment propagation.
+    ///     This is typically passed in from a `Screen` in its
+    ///     `viewControllerDescription(environment:)` method.
+    ///
+    ///   - build: Closure that produces a new instance of the view controller
+    ///
+    ///   - update: Closure that updates the given view controller
+    @_spi(DynamicControllerTypes)
+    public init(
+        performInitialUpdate: Bool = true,
+        dynamicType: UIViewController.Type,
+        environment: ViewEnvironment,
+        build: @escaping () -> UIViewController,
+        update: @escaping (UIViewController) -> Void
+    ) {
+        self.performInitialUpdate = performInitialUpdate
+
+        self.kind = .init(dynamicType: dynamicType)
+
+        self.environment = environment
+
+        self.build = {
+            let viewController = build()
+            guard viewController.isKind(of: dynamicType) else {
+                fatalError("Error creating \(viewController), expecting a \(dynamicType)")
+            }
+            return viewController
+        }
+
+        self.update = { untypedViewController in
+            guard untypedViewController.isKind(of: dynamicType) else {
+                fatalError("Unable to update \(untypedViewController), expecting a \(dynamicType)")
+            }
+            update(untypedViewController)
+        }
+    }
+
     /// Construct and update a new view controller as described by this view controller description.
     /// The view controller will be updated before it is returned, so it is fully configured and prepared for display.
     public func buildViewController() -> UIViewController {
@@ -197,6 +247,12 @@ extension ViewControllerDescription {
             self.checkViewControllerType = { $0 is VC }
         }
 
+        /// This initializer uses dynamic type inspection in `checkViewControllerType`.
+        fileprivate init(dynamicType: UIViewController.Type) {
+            self.viewControllerType = dynamicType
+            self.checkViewControllerType = { $0.isKind(of: dynamicType) }
+        }
+
         /// If the given view controller is of the correct type to be updated by this view controller description.
         ///
         /// If your view controller type can change between updates, call this method before invoking `update(viewController:)`.

WorkflowUI/Tests/ViewControllerDescriptionTests.swift

@@ -20,9 +20,11 @@ import XCTest
 
 import ReactiveSwift
 import Workflow
-@testable import WorkflowUI
+@_spi(DynamicControllerTypes) @testable import WorkflowUI
 
 fileprivate class BlankViewController: UIViewController {}
+fileprivate class BlankViewControllerSubclass: BlankViewController {}
+fileprivate class SecondBlankViewController: UIViewController {}
 
 @objc fileprivate protocol MyProtocol {
     func update()
@@ -203,6 +205,76 @@ class ViewControllerDescriptionTests: XCTestCase {
         let viewControllerAgain = description.buildViewController()
         XCTAssertFalse(viewController === viewControllerAgain)
     }
+
+    func test_viewControllerTypes() {
+        func polymorphicController() -> UIViewController { BlankViewController() }
+        let controller = polymorphicController()
+
+        // Case 1: Dynamic type inspection.
+        // kind.viewControllerType == BlankViewController.self.
+        let descriptionWithDynamicType = ViewControllerDescription(
+            dynamicType: type(of: controller),
+            environment: .empty,
+            build: { controller },
+            update: { _ in }
+        )
+        // canUpdate(viewController:) will evaluate to true for matching UIViewController types or subclasses.
+        XCTAssertTrue(descriptionWithDynamicType.canUpdate(viewController: polymorphicController()))
+        XCTAssertTrue(descriptionWithDynamicType.canUpdate(viewController: BlankViewController()))
+        XCTAssertFalse(descriptionWithDynamicType.canUpdate(viewController: UIViewController()))
+        XCTAssertFalse(descriptionWithDynamicType.canUpdate(viewController: SecondBlankViewController()))
+        XCTAssertTrue(descriptionWithDynamicType.canUpdate(viewController: BlankViewControllerSubclass()))
+
+        // Case 2: Example of static types losing granularity when supplying a superclass type.
+        // kind.viewControllerType == UIViewController.self.
+        let descriptionWithStaticSupertype = ViewControllerDescription(
+            type: type(of: controller),
+            environment: .empty,
+            build: { controller },
+            update: { _ in }
+        )
+        // canUpdate(viewController:) evaluates to true for any UIViewController type.
+        XCTAssertTrue(descriptionWithStaticSupertype.canUpdate(viewController: polymorphicController()))
+        XCTAssertTrue(descriptionWithStaticSupertype.canUpdate(viewController: BlankViewController()))
+        XCTAssertTrue(descriptionWithStaticSupertype.canUpdate(viewController: UIViewController()))
+        XCTAssertTrue(descriptionWithStaticSupertype.canUpdate(viewController: SecondBlankViewController()))
+        XCTAssertTrue(descriptionWithStaticSupertype.canUpdate(viewController: BlankViewControllerSubclass()))
+
+        // Case 3: Common/standard Workflow use case with static types.
+        // kind.viewControllerType == BlankViewController.self.
+        let descriptionWithStaticSubtype = ViewControllerDescription(
+            type: BlankViewController.self,
+            environment: .empty,
+            build: { BlankViewController() },
+            update: { _ in }
+        )
+        // canUpdate(viewController:) will evaluate to true for matching UIViewController types or subclasses.
+        XCTAssertTrue(descriptionWithStaticSubtype.canUpdate(viewController: polymorphicController()))
+        XCTAssertTrue(descriptionWithStaticSubtype.canUpdate(viewController: BlankViewController()))
+        XCTAssertFalse(descriptionWithStaticSubtype.canUpdate(viewController: UIViewController()))
+        XCTAssertFalse(descriptionWithStaticSubtype.canUpdate(viewController: SecondBlankViewController()))
+        XCTAssertTrue(descriptionWithStaticSubtype.canUpdate(viewController: BlankViewControllerSubclass()))
+    }
+
+    func test_buildingWithDynamicType() {
+        let descriptionWithSuperclassType = ViewControllerDescription(
+            dynamicType: BlankViewController.self,
+            environment: .empty,
+            build: { BlankViewControllerSubclass() },
+            update: { _ in }
+        )
+        XCTAssertTrue(descriptionWithSuperclassType.buildViewController().isKind(of: BlankViewController.self))
+        XCTAssertTrue(descriptionWithSuperclassType.buildViewController().isKind(of: BlankViewControllerSubclass.self))
+
+        let descriptionWithExactType = ViewControllerDescription(
+            dynamicType: BlankViewController.self,
+            environment: .empty,
+            build: { BlankViewController() },
+            update: { _ in }
+        )
+        XCTAssertTrue(descriptionWithExactType.buildViewController().isKind(of: BlankViewController.self))
+        XCTAssertFalse(descriptionWithExactType.buildViewController().isKind(of: BlankViewControllerSubclass.self))
+    }
 }
 
 class ViewControllerDescription_KindIdentifierTests: XCTestCase {