Error message if token symbol length too long

src/lib/circuit_value.ts

@@ -2,7 +2,6 @@ import 'reflect-metadata';
 import { Circuit, JSONValue, ProvablePure, Provable } from '../snarky.js';
 import { Field, Bool } from './core.js';
 import { Context } from './global-context.js';
-import { HashInput } from './hash.js';
 import { inCheckedComputation, snarkContext } from './proof_system.js';
 
 // external API
@@ -33,6 +32,7 @@ export {
   witness,
   InferCircuitValue,
   Provables,
+  HashInput,
 };
 
 type Constructor<T> = new (...args: any) => T;
@@ -43,6 +43,22 @@ type NonMethodKeys<T> = {
 }[keyof T];
 type NonMethods<T> = Pick<T, NonMethodKeys<T>>;
 
+type HashInput = { fields?: Field[]; packed?: [Field, number][] };
+const HashInput = {
+  get empty() {
+    return {};
+  },
+  append(input1: HashInput, input2: HashInput) {
+    if (input2.fields !== undefined) {
+      (input1.fields ??= []).push(...input2.fields);
+    }
+    if (input2.packed !== undefined) {
+      (input1.packed ??= []).push(...input2.packed);
+    }
+    return input1;
+  },
+};
+
 /**
  * @deprecated `CircuitValue` is deprecated in favor of {@link Struct}, which features a simpler API and better typing.
  */

src/lib/hash.ts

@@ -1,4 +1,4 @@
-import { ProvableExtended } from './circuit_value.js';
+import { HashInput, ProvableExtended, Struct } from './circuit_value.js';
 import { Poseidon as Poseidon_, Field } from '../snarky.js';
 import { inCheckedComputation } from './proof_system.js';
 
@@ -121,25 +121,10 @@ function packToFields({ fields = [], packed = [] }: HashInput) {
   return fields.concat(packedBits);
 }
 
-type HashInput = { fields?: Field[]; packed?: [Field, number][] };
-const HashInput = {
-  get empty() {
-    return {};
-  },
-  append(input1: HashInput, input2: HashInput) {
-    if (input2.fields !== undefined) {
-      (input1.fields ??= []).push(...input2.fields);
-    }
-    if (input2.packed !== undefined) {
-      (input1.packed ??= []).push(...input2.packed);
-    }
-    return input1;
-  },
-};
-
-type TokenSymbol = { symbol: string; field: Field };
-
-const TokenSymbolPure: ProvableExtended<TokenSymbol, string> = {
+const TokenSymbolPure: ProvableExtended<
+  { symbol: string; field: Field },
+  string
+> = {
   toFields({ field }) {
     return [field];
   },
@@ -163,17 +148,18 @@ const TokenSymbolPure: ProvableExtended<TokenSymbol, string> = {
     return { packed: [[field, 48]] };
   },
 };
-const TokenSymbol = {
-  ...TokenSymbolPure,
-  get empty() {
+class TokenSymbol extends Struct(TokenSymbolPure) {
+  static get empty() {
     return { symbol: '', field: Field.zero };
-  },
+  }
 
-  from(symbol: string): TokenSymbol {
+  static from(symbol: string): TokenSymbol {
+    if (symbol.length > 6)
+      throw Error('Token symbol length should be a maximum of 6');
     let field = prefixToField(symbol);
     return { symbol, field };
-  },
-};
+  }
+}
 
 function emptyReceiptChainHash() {
   return emptyHashWithPrefix('CodaReceiptEmpty');

src/lib/token.test.ts

@@ -16,7 +16,7 @@ import {
   Ledger,
 } from 'snarkyjs';
 
-const tokenSymbol = 'MY_TOKEN';
+const tokenSymbol = 'TOKEN';
 
 class TokenContract extends SmartContract {
   @state(UInt64) totalAmountInCirculation = State<UInt64>();