src/Composer/Downloader/DownloadManager.php
public function setDownloader($type, DownloaderInterface $downloader)
    {
        $type = strtolower($type);
        $this->downloaders[$type] = $downloader;

        return $this;
    }
public function setDownloader($type, DownloaderInterface $downloader)
    {
        $type = strtolower($type);
        $this->downloaders[$type] = $downloader;

        return $this;
    }
Sets installer downloader for a specific installation type.

@param  string              $type       installation type
@param  DownloaderInterface $downloader downloader instance
@return DownloadManager