Support number-keyed records in record() and Describe

src/structs/types.ts

@@ -364,7 +364,7 @@ export function optional<T, S>(struct: Struct<T, S>): Struct<T | undefined, S> {
  * Like TypeScript's `Record` utility.
  */
 
-export function record<K extends string, V>(
+export function record<K extends string | number, V>(
   Key: Struct<K>,
   Value: Struct<V>
 ): Struct<Record<K, V>, null> {

src/utils.ts

@@ -242,7 +242,9 @@ export type IsExactMatch<T, U> =
 export type IsRecord<T> = T extends object
   ? string extends keyof T
     ? T
-    : never
+    : number extends keyof T
+      ? T
+      : never
   : never
 /**
  * Check if a type is a tuple.

test/typings/describe.ts

@@ -126,6 +126,10 @@ test<Describe<Record<string, number>>>((x) => {
   return record(string(), number())
 })
 
+test<Describe<Record<number, number>>>((x) => {
+  return record(number(), number())
+})
+
 test<Describe<RegExp>>((x) => {
   return regexp()
 })

test/typings/record.ts

@@ -5,3 +5,8 @@ test<Record<string, number>>((x) => {
   assert(x, record(string(), number()))
   return x
 })
+
+test<Record<number, number>>((x) => {
+  assert(x, record(number(), number()))
+  return x
+})