Add default container implementation for widgets

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

@@ -176,6 +176,21 @@ public enum UpdateStrategy {
 
 extension Widget {
 
+    /// The view storage.
+    /// - Parameters:
+    ///     - data: Modify views before being updated.
+    ///     - type: The view render data type.
+    /// - Returns: The view storage.
+    func container<Data>(
+        data: WidgetData,
+        type: Data.Type
+    ) -> ViewStorage where Data: ViewRenderData {
+        let storage = ViewStorage(initializeWidget())
+        initProperties(storage, data: data, type: type)
+        update(storage, data: data, updateProperties: true, type: type)
+        return storage
+    }
+
     /// Update the stored content.
     /// - Parameters:
     ///     - storage: The storage to update.

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

@@ -34,6 +34,13 @@ public protocol Widget: AnyView {
         type: Data.Type
     ) where Data: ViewRenderData
 
+    /// Get the widget.
+    /// - Returns: The widget.
+    ///
+    /// Define this function only if you do not define ``Widget/container(data:type:)``.
+    /// Otherwise, it will not have an effect.
+    func initializeWidget() -> Any
+
 }
 
 /// Extend the widget type.
@@ -42,4 +49,10 @@ extension Widget {
     /// A widget's view is empty.
     public var viewContent: Body { [] }
 
+    /// Print a warning if the widget does not set this function but it gets accessed.
+    /// - Returns: A dummy pointer.
+    public func initializeWidget() -> Any {
+        ""
+    }
+
 }