Add support for conditional and optional views

Sources/Model/Extensions/Array.swift

@@ -26,9 +26,7 @@ extension Array: AnyView where Element == AnyView {
         } else {
             var modified = self
             for (index, view) in modified.enumerated() {
-                for modifier in modifiers {
-                    modified[safe: index] = modifier(view)
-                }
+                modified[safe: index] = view.getModified(modifiers: modifiers, type: type)
             }
             return Data.WrapperType { modified }
         }

Sources/Model/User Interface/View/AnyView.swift

@@ -15,11 +15,14 @@ public protocol AnyView {
 
 extension AnyView {
 
-    func getModified(modifiers: [(AnyView) -> AnyView]) -> AnyView {
+    func getModified<Data>(modifiers: [(AnyView) -> AnyView], type: Data.Type) -> AnyView where Data: ViewRenderData {
         var modified: AnyView = self
         for modifier in modifiers {
             modified = modifier(modified)
         }
+        if let dummy = modified as? DummyEitherView {
+            modified = type.EitherViewType(dummy.condition) { dummy.view1 ?? [] } else: { dummy.view2 ?? [] }
+        }
         return modified
     }
 
@@ -55,19 +58,19 @@ extension AnyView {
     /// - Parameter modifiers: Modify views before being updated.
     /// - Returns: The widget.
     func widget<Data>(modifiers: [(AnyView) -> AnyView], type: Data.Type) -> Widget where Data: ViewRenderData {
-        let modified = getModified(modifiers: modifiers)
+        let modified = getModified(modifiers: modifiers, type: type)
         if let peer = modified as? Widget {
             return peer
         }
         if let array = modified as? Body {
             return Data.WrapperType { array }
         }
-        return Data.WrapperType { viewContent.map { $0.getModified(modifiers: modifiers) } }
+        return Data.WrapperType { viewContent.map { $0.getModified(modifiers: modifiers, type: type) } }
     }
 
     /// Whether the view can be rendered in a certain environment.
     func renderable<Data>(type: Data.Type, modifiers: [(AnyView) -> AnyView]) -> Bool where Data: ViewRenderData {
-        let result = getModified(modifiers: modifiers)
+        let result = getModified(modifiers: modifiers, type: type)
         return result as? Data.WidgetType != nil
         || result as? SimpleView != nil
         || result as? View != nil

Sources/Model/User Interface/View/EitherView.swift

@@ -0,0 +1,22 @@
+//
+//  EitherView.swift
+//  Meta
+//
+//  Created by david-swift on 06.08.24.
+//
+
+/// A view building conditional bodies.
+public protocol EitherView: AnyView {
+
+    /// Initialize the either view.
+    /// - Parameters:
+    ///     - condition: Whether the first view is visible-
+    ///     - view1: The first view, visible if true.
+    ///     - view2: The second view, visible if false.
+    init(
+        _ condition: Bool,
+        @ViewBuilder view1: () -> Body,
+        @ViewBuilder else view2: () -> Body
+    )
+
+}

Sources/Model/User Interface/View/ViewBuilder.swift

@@ -53,6 +53,27 @@ public enum ViewBuilder {
         component
     }
 
+    /// Enables support for `if` statements without an `else`.
+    /// - Parameter component: An optional component.
+    /// - Returns: A nonoptional component.
+    public static func buildOptional(_ component: Component?) -> Component {
+        .element(DummyEitherView(condition: component != nil, view1: buildFinalResult(component ?? .element([]))))
+    }
+
+    /// Enables support for `if`-`else` and `switch` statements.
+    /// - Parameter component: A component.
+    /// - Returns: The component.
+    public static func buildEither(first component: Component) -> Component {
+        .element(DummyEitherView(condition: true, view1: buildFinalResult(component)))
+    }
+
+    /// Enables support for `if`-`else` and `switch` statements.
+    /// - Parameter component: A component.
+    /// - Returns: The component.
+    public static func buildEither(second component: Component) -> Component {
+        .element(DummyEitherView(condition: false, view2: buildFinalResult(component)))
+    }
+
     /// Convert a component to an array of elements.
     /// - Parameter component: The component to convert.
     /// - Returns: The generated array of elements.

Sources/Model/User Interface/View/ViewRenderData.swift

@@ -12,5 +12,7 @@ public protocol ViewRenderData {
     associatedtype WidgetType
     /// The wrapper widget.
     associatedtype WrapperType: Wrapper
+    /// The type replacing dummy either views.
+    associatedtype EitherViewType: EitherView
 
 }

Sources/View/DummyEitherView.swift

@@ -0,0 +1,21 @@
+//
+//  DummyEitherView.swift
+//  Meta
+//
+//  Created by david-swift on 06.08.24.
+//
+
+/// A dummy either view. This will be replaced by the platform-specific either view.
+struct DummyEitherView: SimpleView {
+
+    /// Whether to present the first view.
+    var condition: Bool
+    /// The first view.
+    var view1: Body?
+    /// The second view.
+    var view2: Body?
+
+    /// By default, show the first view.
+    var view: Body { view1 ?? view2 ?? [] }
+
+}

Tests/DemoApp/DemoApp.swift

@@ -33,9 +33,14 @@ struct DemoView: View {
 
     @State private var model = TestModel()
     var app: any AppStorage
+    let condition = false
 
     var view: Body {
-        Backend1.TestWidget1()
+        if condition {
+            Backend1.TestWidget1()
+        } else {
+            Backend1.TestWidget3()
+        }
         Backend1.Button(model.test) {
             Task {
                 app.addSceneElement("main")

Tests/SampleBackends/Backend1.swift

@@ -131,10 +131,25 @@ public enum Backend1 {
 
     }
 
+    public struct EitherView: BackendWidget, Meta.EitherView {
+
+        public init(_ condition: Bool, view1: () -> Body, else view2: () -> Body) {
+        }
+
+        public func container<Data>(modifiers: [(any AnyView) -> any AnyView], type: Data.Type) -> ViewStorage where Data : ViewRenderData {
+            .init(nil)
+        }
+
+        public func update<Data>(_ storage: ViewStorage, modifiers: [(any AnyView) -> any AnyView], updateProperties: Bool, type: Data.Type) where Data : ViewRenderData {
+        }
+
+    }
+
     public struct MainViewRenderData: ViewRenderData {
 
         public typealias WidgetType = BackendWidget
         public typealias WrapperType = Wrapper
+        public typealias EitherViewType = EitherView
 
     }