Lazy decoration (part 4, lazyMethod/lazyMethods) (#4144)

packages/types/src/create/index.ts

@@ -5,5 +5,6 @@ export * from './createClass';
 export * from './createType';
 export * from './encodeTypes';
 export * from './getTypeDef';
+export * from './lazy';
 export * from './registry';
 export * from './typeSplit';

packages/types/src/create/lazy.ts

@@ -0,0 +1,29 @@
+// Copyright 2017-2021 @polkadot/types authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+type WithToString = { toString: () => string };
+
+export function lazyMethod <T, K> (result: Record<string, T>, item: K, creator: (d: K) => T, getName?: (d: K) => string): void {
+  let cached: T | null = null;
+
+  Object.defineProperty(result, getName ? getName(item) : (item as WithToString).toString(), {
+    enumerable: true,
+    get: (): T => {
+      if (!cached) {
+        cached = creator(item);
+      }
+
+      return cached;
+    }
+  });
+}
+
+export function lazyMethods <T, K> (items: K[], creator: (v: K) => T, getName?: (m: K) => string): Record<string, T> {
+  const result: Record<string, T> = {};
+
+  for (let i = 0; i < items.length; i++) {
+    lazyMethod(result, items[i], creator, getName);
+  }
+
+  return result;
+}