First check-in of the code from the Obsidian Prj project.

src/decorators/RegisterInstance.ts

@@ -0,0 +1,70 @@
+import { DIContainer } from '../DIContainer';
+import { InitDelegate } from '../types/InitDelegate';
+
+/**
+ * A decorator to register an instance of a class in the DI (Dependency Injection) container.
+ * The instance is created only when it is first needed (Lazy Initialization).
+ * @template TargetType The type of the class whose instance is to be registered.
+ * @param identifier The identifier used to register the instance in the DI container.
+ * @param init An optional initializer function which get the constructor of the class
+ * as input and returns an instance of the class.
+ * @returns A function that is applied as a decorator to the class.
+ * @example
+ * ```ts
+ * \@RegisterInstance('MyClassInstanceIdentifier', arg1, arg2)
+ * class MyClass {
+ *   // ...
+ * }
+ * ```
+ */
+export function RegisterInstance<
+    TargetType extends new (..._args: unknown[]) => InstanceType<TargetType>,
+>(
+    identifier: string,
+    init?: InitDelegate<
+        TargetType & { new (..._args: unknown[]): InstanceType<TargetType> },
+        InstanceType<TargetType>
+    >,
+) {
+    return function (constructor: TargetType, ...args: unknown[]): void {
+        // Get the instance of the DI container
+        const diContainer = DIContainer.getInstance();
+
+        // Create a proxy to instantiate the class when needed (Lazy Initialization)
+        let lazyProxy: unknown = new Proxy(
+            {},
+            {
+                get(target, prop, receiver) {
+                    let instance: InstanceType<TargetType>;
+
+                    if (init) {
+                        instance = init(constructor);
+                    } else {
+                        instance = new constructor(...args);
+                    }
+                    lazyProxy = instance;
+
+                    // Return the requested property of the instance
+                    return instance[prop as keyof InstanceType<TargetType>];
+                },
+                set(target, prop, value, receiver) {
+                    let instance: InstanceType<TargetType>;
+
+                    if (init) {
+                        instance = init(constructor);
+                    } else {
+                        instance = new constructor(...args);
+                    }
+                    lazyProxy = instance;
+
+                    // Set the requested property of the instance
+                    return (instance[prop as keyof InstanceType<TargetType>] =
+                        value);
+                },
+            },
+        );
+
+        // Register the lazy proxy in the DI container
+        diContainer.register(identifier, lazyProxy);
+    };
+}