support get lazy

src/app-context/app-context.ts

@@ -189,11 +189,24 @@ export class AppContextCore<Cur = Empty, Req = Empty> {
     return this as any;
   }
 
-  get<R>(cls: AppServiceClass<Cur, Req, any, R>): R {
-    const key = cls as unknown as AnyClass;
+  get<R>(
+    cls:
+      | AppServiceClass<Cur, Req, any, R>
+      | (() => AppServiceClass<Cur, Req, any, R>),
+  ): R {
+    let key = cls as unknown as AnyClass;
+    if (
+      !this.registry.has(key) &&
+      typeof cls === 'function' &&
+      !(cls as any).prototype
+    ) {
+      key = (cls as () => AppServiceClass<Cur, Req, any, R>)() as AnyClass;
+    }
+
     if (!this.registry.has(key)) {
-      throw new Error(`Service not provided: ${cls.name}`);
+      throw new Error(`Service not provided: ${key?.name ?? cls.name}`);
     }
+
     const entry = this.registry.get(key)!;
     const inst = entry.inst;
     if (isPromiseLike(inst)) {