src/Container.php
public function set($id, $service)
    {
        $id = strtolower($id);

        $this->services[$id] = $service;

        return $this;
    }
public function set($id, $service)
    {
        $id = strtolower($id);

        $this->services[$id] = $service;

        return $this;
    }
Set a service instance

@param string $id      Service id
@param mixed  $service Service instance

@return Container