src/Composer/Installer/InstallationManager.php
public function getInstallPath(PackageInterface $package)
    {
        $installer = $this->getInstaller($package->getType());

        return $installer->getInstallPath($package);
    }
public function getInstallPath(PackageInterface $package)
    {
        $installer = $this->getInstaller($package->getType());

        return $installer->getInstallPath($package);
    }
Returns the installation path of a package

@param  PackageInterface $package
@return string           path