Added an interface as alluded to in the docs

src/Database/Type.php

@@ -21,7 +21,7 @@
  * Encapsulates all conversion functions for values coming from database into PHP and
  * going from PHP into database.
  */
-class Type
+class Type implements TypeInterface
 {
 
     /**

src/Database/TypeInterface.php

@@ -0,0 +1,61 @@
+<?php
+/**
+ * CakePHP(tm) : Rapid Development Framework (http://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ * @link          http://cakephp.org CakePHP(tm) Project
+ * @since         3.3.0
+ * @license       http://www.opensource.org/licenses/mit-license.php MIT License
+ */
+namespace Cake\Database;
+
+/**
+ * Encapsulates all conversion functions for values coming from database into PHP and
+ * going from PHP into database.
+ */
+interface TypeInterface
+{
+
+    /**
+     * Casts given value from a PHP type to one acceptable by database
+     *
+     * @param mixed $value value to be converted to database equivalent
+     * @param \Cake\Database\Driver $driver object from which database preferences and configuration will be extracted
+     * @return mixed
+     */
+    public function toDatabase($value, Driver $driver);
+
+    /**
+     * Casts given value from a database type to PHP equivalent
+     *
+     * @param mixed $value value to be converted to PHP equivalent
+     * @param \Cake\Database\Driver $driver object from which database preferences and configuration will be extracted
+     * @return mixed
+     */
+    public function toPHP($value, Driver $driver);
+
+    /**
+     * Casts give value to Statement equivalent
+     *
+     * @param mixed $value value to be converted to PHP equivalent
+     * @param \Cake\Database\Driver $driver object from which database preferences and configuration will be extracted
+     * @return mixed
+     */
+    public function toStatement($value, Driver $driver);
+
+    /**
+     * Marshalls flat data into PHP objects.
+     *
+     * Most useful for converting request data into PHP objects
+     * that make sense for the rest of the ORM/Database layers.
+     *
+     * @param mixed $value The value to convert.
+     * @return mixed Converted value.
+     */
+    public function marshal($value);
+}