public function getOperation($name)
    {
        if (!isset($this->operations[$name])) {
            if (!isset($this->definition['operations'][$name])) {
                throw new \InvalidArgumentException("Unknown operation: $name");
            }
            $this->operations[$name] = new Operation(
                $this->definition['operations'][$name],
                $this->shapeMap
            );
        }

        return $this->operations[$name];
    }