Preserve contract prototypes when extending, add cache property to …

…cached contracts (#42)

* Add clarifying comment

* Add cache propoerty to cached contract

* Preserve prototypes when extending

* Add changeset

* typo

.changeset/lazy-scissors-teach.md

@@ -0,0 +1,5 @@
+---
+"@delvtech/evm-client": patch
+---
+
+Added a `cache` property to the `CachedReadContract` type and ensured the factories preserve the prototypes of the contract's they're given.

packages/evm-client/src/contract/factories/createCachedReadContract.ts

@@ -33,8 +33,16 @@ export function createCachedReadContract<TAbi extends Abi = Abi>({
   cache = createLruSimpleCache({ max: DEFAULT_CACHE_SIZE }),
   namespace,
 }: CreateCachedReadContractOptions<TAbi>): CachedReadContract<TAbi> {
-  return {
-    ...contract,
+  // Because this is part of the public API, we won't know if the original
+  // contract is a plain object or a class instance, so we use Object.create to
+  // preserve the original contract's prototype chain when extending, ensuring
+  // the new contract includes all the original contract's methods and
+  // instanceof checks will still work.
+  const contractPrototype = Object.getPrototypeOf(contract);
+  const newContract = Object.create(contractPrototype);
+
+  const overrides: Partial<CachedReadContract<TAbi>> = {
+    cache,
 
     /**
      * Reads data from the contract. First checks the cache, and if not present,
@@ -111,6 +119,8 @@ export function createCachedReadContract<TAbi extends Abi = Abi>({
       cache.clear();
     },
   };
+
+  return Object.assign(newContract, contract, overrides);
 }
 
 async function getOrSet<TValue>({

packages/evm-client/src/contract/factories/createCachedReadWriteContract.ts

@@ -8,7 +8,7 @@ import { ReadWriteContract } from 'src/contract/types/Contract';
 
 export interface CreateCachedReadWriteContractOptions<TAbi extends Abi = Abi>
   extends CreateCachedReadContractOptions<TAbi> {
-  contract: ReadWriteContract<TAbi> | CachedReadWriteContract<TAbi>;
+  contract: ReadWriteContract<TAbi>;
 }
 
 /**
@@ -22,18 +22,25 @@ export function createCachedReadWriteContract<TAbi extends Abi = Abi>({
   cache,
   namespace,
 }: CreateCachedReadWriteContractOptions<TAbi>): CachedReadWriteContract<TAbi> {
-  const cachedReadContract = isCached(contract)
-    ? contract
-    : createCachedReadContract({ contract, cache, namespace });
-
-  return {
-    ...contract,
-    ...cachedReadContract,
-  };
+  // Avoid double-caching if given a contract that already has a cache.
+  if (isCached(contract)) {
+    return contract;
+  }
+  // Because this is part of the public API, we won't know if the original
+  // contract is a plain object or a class instance, so we use Object.create to
+  // preserve the original contract's prototype chain when extending, ensuring
+  // the new contract includes all the original contract's methods and
+  // instanceof checks will still work.
+  const contractPrototype = Object.getPrototypeOf(contract);
+  const newContract = Object.create(contractPrototype);
+  return Object.assign(
+    newContract,
+    createCachedReadContract({ contract, cache, namespace }),
+  );
 }
 
 function isCached<TAbi extends Abi>(
-  contract: ReadWriteContract<TAbi> | CachedReadWriteContract<TAbi>,
+  contract: ReadWriteContract<TAbi>,
 ): contract is CachedReadWriteContract<TAbi> {
   return 'clearCache' in contract;
 }

packages/evm-client/src/contract/types/CachedContract.ts

@@ -5,9 +5,11 @@ import {
   ReadWriteContract,
 } from 'src/contract/types/Contract';
 import { FunctionName } from 'src/contract/types/Function';
+import { SimpleCache } from 'src/exports';
 
 export interface CachedReadContract<TAbi extends Abi = Abi>
   extends ReadContract<TAbi> {
+  cache: SimpleCache;
   namespace?: string;
   clearCache(): void;
   deleteRead<TFunctionName extends FunctionName<TAbi>>(