private static function getInstalled()
    {
        if (null === self::$canGetVendors) {
            self::$canGetVendors = method_exists('Composer\Autoload\ClassLoader', 'getRegisteredLoaders');
        }

        $installed = array();

        if (self::$canGetVendors) {
            foreach (ClassLoader::getRegisteredLoaders() as $vendorDir => $loader) {
                if (isset(self::$installedByVendor[$vendorDir])) {
                    $installed[] = self::$installedByVendor[$vendorDir];
                } elseif (is_file($vendorDir.'/composer/installed.php')) {
                    $installed[] = self::$installedByVendor[$vendorDir] = require $vendorDir.'/composer/installed.php';
                    if (null === self::$installed && strtr($vendorDir.'/composer', '\\', '/') === strtr(__DIR__, '\\', '/')) {
                        self::$installed = $installed[count($installed) - 1];
                    }
                }
            }
        }

        if (null === self::$installed) {
            // only require the installed.php file if this file is loaded from its dumped location,
            // and not from its source location in the composer/composer package, see https://github.com/composer/composer/issues/9937
            if (substr(__DIR__, -8, 1) !== 'C') {
                self::$installed = require __DIR__ . '/installed.php';
            } else {
                self::$installed = array();
            }
        }
        $installed[] = self::$installed;

        return $installed;
    }