private function buildCallback($type, $object)
    {
        if (!array_key_exists($type, $this->callbacks)) {
            return null;
        }

        $callback = $this->callbacks[$type];

        if (is_callable($callback) or is_callable([$object, $callback])) {
            return $callback;
        }

        if (is_string($callback)) {
            return $this->buildExpressionCallback($type, $object, $callback);
        }

        throw new \InvalidArgumentException(sprintf('Callback for type "%s" is not a valid callback.', $type));
    }
private function buildCallback($type, $object)
    {
        if (!array_key_exists($type, $this->callbacks)) {
            return null;
        }

        $callback = $this->callbacks[$type];

        if (is_callable($callback) or is_callable([$object, $callback])) {
            return $callback;
        }

        if (is_string($callback)) {
            return $this->buildExpressionCallback($type, $object, $callback);
        }

        throw new \InvalidArgumentException(sprintf('Callback for type "%s" is not a valid callback.', $type));
    }
private function buildCallback ( $ type , $ object ) { if ( ! array_key_exists ( $ type , $ this -> callbacks ) ) { return null ; } $ callback = $ this -> callbacks [ $ type ] ; if ( is_callable ( $ callback ) or is_callable ( [ $ object , $ callback ] ) ) { return $ callback ; } if ( is_string ( $ callback ) ) { return $ this -> buildExpressionCallback ( $ type , $ object , $ callback ) ; } throw new \ InvalidArgumentException ( sprintf ( 'Callback for type "%s" is not a valid callback.' , $ type ) ) ; }
Builds and initialises a callback.

@param string $type
@param object $object

@return callable|string|ExpressionLanguage|null
Builds and initialises a callback .