do an array_search instead of an in_array at construct and save the k…

…ey found so that getKey will not require an extra array search

src/Enum.php

@@ -28,6 +28,13 @@ abstract class Enum implements \JsonSerializable
      */
     protected $value;
 
+    /**
+     * Enum key, the constant name
+     *
+     * @var string
+     */
+    protected $key;
+
     /**
      * Store existing constants in a static cache per object.
      *
@@ -61,12 +68,13 @@ public function __construct($value)
             $value = $value->getValue();
         }
 
-        if (!$this->isValid($value)) {
+        if (false === ($key = static::search($value))) {
             throw new \UnexpectedValueException("Value '$value' is not part of the enum " . static::class);
         }
 
         /** @psalm-var T */
         $this->value = $value;
+        $this->key = $key;
     }
 
     /**
@@ -86,7 +94,7 @@ public function getValue()
      */
     public function getKey(): string
     {
-        return static::search($this->value);
+        return $this->key;
     }
 
     /**