Introducing new functions¶

Just like with keys, it is possible to use a hook to introduce custom functions, which makes it possible to do pretty much whatever one wants with expressions. An example class is provided in Classes/Sample/FunctionProcessor.php . It introduces a function called "offset". To make this function available, it must be registered as follows:

$GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['expressions']['customFunction']['offset'] = 'Cobweb\\Expressions\\Sample\\FunctionProcessor->offset';

The function itself looks like this:

public function offset($parameters, $parentObject) {
        $value = intval($parameters[0]);
        $offset = 0;
        if (isset($parameters[1])) {
                $offset = intval($parameters[1]);
        }
        return $value + $offset;
}

It receives an array containing the function call parameters and what would normally be a back-reference to the calling object, but is actually a dummy object, since the \Cobweb\Expressions\ExpressionParser class is purely static. The call parameters array is an indexed array containing:

• at index 0, the value that was calculated from the expression
• at index 1 and more, any additional parameters that were defined in the function call.

As an example, consider the following expression using this custom function:

gp:foo->offset:5

The offset() method will receive the value of "gp:foo" in $parameters[0] and "5" in $parameters[1].

The function is expected to return the modified value, or the original value from the expression if no change happened.