Pass through value failure

src/result.ts

@@ -30,7 +30,13 @@ export type Failure = {
   /**
    * A key indicating the location at which validation failed.
    */
-  key: string;
+  key?: string;
+
+  /**
+   * The original value passed through so data inspection can be done after failure.
+   * value is `any` here because its argument in `validate` is `any` type.
+   */
+  valueInvalidated: any;
 };
 
 /**

src/runtype.ts

@@ -117,7 +117,7 @@ export function create<A extends Runtype>(check: (x: {}) => Static<A>, A: any):
       check(value);
       return { success: true, value };
     } catch ({ message, key }) {
-      return { success: false, message, key };
+      return { success: false, message, key, valueInvalidated: value };
     }
   }