Merge pull request #1731 from kantp/kantp/expose-max-account-updates

Expose `MAX_ACCOUNT_UPDATES` from `TokenContract.ts`

src/lib/mina/token/token-contract.ts

@@ -13,11 +13,7 @@ import { DeployArgs, SmartContract } from '../zkapp.js';
 import { TokenAccountUpdateIterator } from './forest-iterator.js';
 import { tokenMethods } from './token-methods.js';
 
-export { TokenContract };
-
-// it's fine to have this restriction, because the protocol also has a limit of ~20
-// TODO find out precise protocol limit
-const MAX_ACCOUNT_UPDATES = 20;
+export { TokenContract, TokenContractV2 };
 
 /**
  * Base token contract which
@@ -27,6 +23,10 @@ const MAX_ACCOUNT_UPDATES = 20;
 abstract class TokenContract extends SmartContract {
   // change default permissions - important that token contracts use an access permission
 
+  /** The maximum number of account updates using the token in a single
+   * transaction that this contract supports. */
+  static MAX_ACCOUNT_UPDATES = 20;
+
   /**
    * Deploys a {@link TokenContract}.
    *
@@ -96,16 +96,16 @@ abstract class TokenContract extends SmartContract {
       this.deriveTokenId()
     );
 
-    // iterate through the forest and apply user-defined logc
-    for (let i = 0; i < MAX_ACCOUNT_UPDATES; i++) {
+    // iterate through the forest and apply user-defined logic
+    for (let i = 0; i < (this.constructor as typeof TokenContract).MAX_ACCOUNT_UPDATES; i++) {
       let { accountUpdate, usesThisToken } = iterator.next();
       callback(accountUpdate, usesThisToken);
     }
 
     // prove that we checked all updates
     iterator.assertFinished(
       `Number of account updates to approve exceed ` +
-        `the supported limit of ${MAX_ACCOUNT_UPDATES}.\n`
+        `the supported limit of ${(this.constructor as typeof TokenContract).MAX_ACCOUNT_UPDATES}.\n`
     );
 
     // skip hashing our child account updates in the method wrapper
@@ -179,6 +179,15 @@ abstract class TokenContract extends SmartContract {
   }
 }
 
+/** Version of `TokenContract` with the precise number of `MAX_ACCOUNT_UPDATES`
+ * 
+ * The value of 20 in `TokenContract` was a rough upper limit, the precise upper
+ * bound is 9.
+ */
+abstract class TokenContractV2 extends TokenContract {
+  static MAX_ACCOUNT_UPDATES = 9;
+}
+
 function toForest(
   updates: (AccountUpdate | AccountUpdateTree)[]
 ): AccountUpdateForest {