Implement Stringable interface on Enum

Author: jdecool

composer.json

@@ -36,7 +36,10 @@
             "MabeEnumTest\\":  "tests/MabeEnumTest/",
             "MabeEnumStaticAnalysis\\": "tests/MabeEnumStaticAnalysis/",
             "MabeEnumBench\\": "bench/"
-        }
+        },
+        "classmap": [
+            "stubs/Stringable.php"
+        ]
     },
     "extra": {
         "branch-alias": {

src/Enum.php

@@ -17,7 +17,7 @@
  *
  * @psalm-immutable
  */
-abstract class Enum
+abstract class Enum implements \Stringable
 {
     /**
      * The selected enumerator value

stubs/Stringable.php

@@ -0,0 +1,11 @@
+<?php
+
+if (\PHP_VERSION_ID < 80000) {
+    interface Stringable
+    {
+        /**
+         * @return string
+         */
+        public function __toString();
+    }
+}