feat(enum): add validator for enumerate

Author: TomokiMiyauci

validators/enum.ts

@@ -0,0 +1,20 @@
+import { AssertiveScalarValidator } from "../utils.ts";
+import { displayOr, shouldBeBut } from "./utils.ts";
+
+export class EnumValidator<const T>
+  extends AssertiveScalarValidator<unknown, T> {
+  values: [T, T, ...T[]];
+  constructor(v1: T, v2: T, ...values: readonly T[]) {
+    super();
+    super.expect(shouldBeBut);
+    this.values = [v1, v2, ...values];
+  }
+
+  is(input: unknown): input is T {
+    return (this.values as unknown[]).includes(input);
+  }
+
+  toString(): string {
+    return `one of ${displayOr(...this.values)}`;
+  }
+}