protected function getCacheControlHeader()
    {
        $cacheControl = '';
        foreach ($this->cacheDirectives as $cacheDirective) {
            $cacheControl .= ($cacheDirective !== '' ? $cacheDirective . ', ' : '');
        }
        $cacheControl = trim($cacheControl, ' ,');
        return ($cacheControl === '' ? null : $cacheControl);
    }
protected function getCacheControlHeader()
    {
        $cacheControl = '';
        foreach ($this->cacheDirectives as $cacheDirective) {
            $cacheControl .= ($cacheDirective !== '' ? $cacheDirective . ', ' : '');
        }
        $cacheControl = trim($cacheControl, ' ,');
        return ($cacheControl === '' ? null : $cacheControl);
    }
protected function getCacheControlHeader ( ) { $ cacheControl = '' ; foreach ( $ this -> cacheDirectives as $ cacheDirective ) { $ cacheControl .= ( $ cacheDirective !== '' ? $ cacheDirective . ', ' : '' ) ; } $ cacheControl = trim ( $ cacheControl , ' ,' ) ; return ( $ cacheControl === '' ? null : $ cacheControl ) ; }
Renders and returns a Cache-Control header, based on the previously set
cache control directives.

@return string Either the value of the header or NULL if it shall be omitted
@see get()
Renders and returns a Cache - Control header based on the previously set cache control directives .