.. _zend.filter.writing_filters:

Writing Filters
===============

``Zend\Filter`` supplies a set of commonly needed filters, but developers will often need to write custom filters
for their particular use cases. The task of writing a custom filter is facilitated by implementing
``Zend\Filter\FilterInterface``.

``Zend\Filter\FilterInterface`` defines a single method, ``filter()``, that may be implemented by user classes.

The following example demonstrates how to write a custom filter:

.. code-block:: php
   :linenos:

   namespace Application\Filter;

   use Zend\Filter\FilterInterface;

   class MyFilter implements FilterInterface
   {
       public function filter($value)
       {
           // perform some transformation upon $value to arrive on $valueFiltered

           return $valueFiltered;
       }
   }

To attach an instance of the filter defined above to a filter chain:

.. code-block:: php
   :linenos:

   $filterChain = new Zend\Filter\FilterChain();
   $filterChain->attach(new Application\Filter\MyFilter());