No need to do preg_quote on a constant.. We know the answer

Author: Nyholm

src/AbstractCachePool.php

@@ -26,13 +26,6 @@ abstract class AbstractCachePool implements CacheItemPoolInterface, TaggablePool
 {
     use TaggablePoolTrait;
 
-    /**
-     * List of invalid (or reserved) key characters.
-     *
-     * @type string
-     */
-    const KEY_INVALID_CHARACTERS = '{}()/\@:';
-
     /**
      * @type CacheItemInterface[] deferred
      */
@@ -245,12 +238,10 @@ protected function validateKey($key)
             ));
         }
 
-        $invalid = preg_quote(static::KEY_INVALID_CHARACTERS, '|');
-        if (preg_match('|['.$invalid.']|', $key)) {
+        if (preg_match('|[\{\}\(\)/\\@\:]|', $key)) {
             throw new InvalidArgumentException(sprintf(
-                'Invalid key: "%s". The key contains one or more characters reserved for future extension: %s',
-                $key,
-                static::KEY_INVALID_CHARACTERS
+                'Invalid key: "%s". The key contains one or more characters reserved for future extension: {}()/\@:',
+                $key
             ));
         }
     }