src/Composer/Autoload/ClassLoader.php
public function setApcuPrefix($apcuPrefix)
    {
        $this->apcuPrefix = function_exists('apcu_fetch') && filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) ? $apcuPrefix : null;
    }
public function setApcuPrefix($apcuPrefix)
    {
        $this->apcuPrefix = function_exists('apcu_fetch') && filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) ? $apcuPrefix : null;
    }
APCu prefix to use to cache found/not-found classes, if the extension is enabled.

@param string|null $apcuPrefix