public function getConstants()
    {
        if ($this->constants === null) {
            $prettyPrinter = new PrettyPrinter\Standard;
            // lazy load class constants list
            $this->constants = array();
            foreach ($this->node->stmts as $stmt) {
                if ($stmt instanceof Node\Stmt\ClassConst) {
                    foreach ($stmt->consts as $const) {
                        $this->constants[$const->name] = trim(
                            $prettyPrinter->prettyPrintExpr($const->value),
                            '"\''
                        );
                    }
                }
            }
        }
        return $this->constants;
    }