Added first files

lib/src/decorators/immutable.ts

@@ -0,0 +1,15 @@
+import { ModelConstructor } from "../interfaces";
+
+export const IMMUTABLE_FIELDS = new WeakMap<ModelConstructor, Set<string>>();
+
+export function immutable(value: unknown, context: ClassFieldDecoratorContext) {
+  context.addInitializer(function () {
+    const ctor = this.constructor as ModelConstructor;
+    let set = IMMUTABLE_FIELDS.get(ctor);
+    if (!set) {
+      set = new Set<string>();
+      IMMUTABLE_FIELDS.set(ctor, set);
+    }
+    set.add(context.name as string);
+  });
+}