gistfile1.php

<?php

namespace Db\Form\InputFilter;

trait Field
{
    abstract public function inputFilterInput();
}


namespace Db\Field;

trait Username
{
    use \Db\Form\InputFilter\Field { inputFilterInput as inputFilterInputUsername; }

    private function inputFilterInputUsername($inputFilter = null) {
        if (!$inputFilter) $inputFilter = new InputFilter();

        return $inputFilter->getFactory()->createInput(array(
            'name' => 'displayName',
            'required' => true,
            'validators' => array(),
        ));
    }
}

results in 
 Class Db\Entity\User contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Db\Entity\User::inputFilterInput)