Trigger notice when Enum instance already exists

src/Enum.php

@@ -73,6 +73,17 @@ public function __toString()
         return (string)$this->value;
     }
 
+    /**
+     * Register object in cache and trigger a notice if it already exists.
+     */
+    public function __wakeup()
+    {
+        $enum = EnumManager::get($this);
+        if ($enum !== $this) {
+            trigger_error("Enum is already initialized", E_USER_NOTICE);
+        }
+    }
+
     /**
      * Compares one Enum with another.
      *

tests/EnumTest.php

@@ -229,4 +229,28 @@ public function testEqualsComparesProblematicValuesProperly()
         $this->assertFalse($emptyString->equals($null));
         $this->assertFalse($null->equals($false));
     }
+
+    /**
+     * __wakeup()
+     */
+    public function testUnserialize()
+    {
+        $ser = 'O:37:"MyCLabs\Tests\Enum\UnserializeFixture":2:{'
+             . 's:23:"#MyCLabs\Enum\Enum#name";s:4:"ONCE";'
+             . 's:24:"#MyCLabs\Enum\Enum#value";s:2:"OK";}';
+        $once = unserialize(strtr($ser, "#", "\0"));
+
+        $this->assertSame($once, UnserializeFixture::ONCE());
+    }
+
+    /**
+     * @expectedException \PHPUnit_Framework_Error_Notice
+     */
+    public function testUnserializeError()
+    {
+        $ser = 'O:30:"MyCLabs\Tests\Enum\EnumFixture":2:{'
+             . 's:23:"#MyCLabs\Enum\Enum#name";s:3:"FOO";'
+             . 's:24:"#MyCLabs\Enum\Enum#value";s:3:"foo";}';
+        $foo = unserialize(strtr($ser, "#", "\0"));
+    }
 }

tests/UnserializeFixture.php

@@ -0,0 +1,19 @@
+<?php
+/**
+ * @link    http://github.com/myclabs/php-enum
+ * @license http://www.opensource.org/licenses/mit-license.php MIT (see the LICENSE file)
+ */
+
+namespace MyCLabs\Tests\Enum;
+
+use MyCLabs\Enum\Enum;
+
+/**
+ * Class UnserializeFixture
+ *
+ * @method static UnserializeFixture ONCE()
+ */
+class UnserializeFixture extends Enum
+{
+    const ONCE = 'OK';
+}