<?php /* #?ini charset="utf-8"?

[ModuleSettings]
ExtensionRepositories[]=mysite_hello

*/ ?>

<?php
$FunctionList = array();

$FunctionList['newest'] = array(
    'name' => 'newest',
    'call_method' => array( 'class' => 'mysiteHelloFunctionCollection',
                            'method' => 'fetchNewest' ),
    'parameters' => array(
        array( 'name' => 'class_identifier', 'type' => 'string', 'required' => true ),
        array( 'name' => 'parent_node_id', 'type' => 'integer', 'required' => false, 'default' => 2 ),
        array( 'name' => 'limit', 'type' => 'integer', 'required' => false, 'default' => 5 )
    )
);

<?php
/**
 * Fetch functions of the module "hello":
 *   fetch( 'hello', 'newest', hash( 'class_identifier', 'article', 'limit', 3 ) )
 */
class mysiteHelloFunctionCollection
{
    public static function fetchNewest( $classIdentifier, $parentNodeID = 2, $limit = 5 )
    {
        $limit = max( 1, min( (int)$limit, 50 ) );
        $nodes = eZContentObjectTreeNode::subTreeByNodeID(
            array( 'ClassFilterType' => 'include',
                   'ClassFilterArray' => array( (string)$classIdentifier ),
                   'SortBy' => array( 'published', false ),
                   'Limit' => $limit ),
            (int)$parentNodeID
        );
        return array( 'result' => is_array( $nodes ) ? $nodes : array() );
    }
}

php -l extension/mysite_hello/modules/hello/function_definition.php
php -l extension/mysite_hello/classes/mysitehellofunctioncollection.php
php bin/php/ezpgenerateautoloads.php -e
php bin/php/ezcache.php --clear-all

{def $newest = fetch( 'hello', 'newest', hash( 'class_identifier', 'article', 'limit', 2 ) )}
{foreach $newest as $node}[{$node.name|wash}]{/foreach}
{fetch( 'hello', 'newest', hash( 'class_identifier', 'nothing_like_this' ) )|count}
{undef $newest}

git -C extension/mysite_hello add modules classes settings
git -C extension/mysite_hello commit -m "Added: The fetch function hello/newest"