parsing - php unexpected ')' parse error

I am trying to set default value for a function. I want the function $expires default value to be time() + 604800.

I am trying

public function set($name,$value,$expires = time()+604800) {
    echo $expires;
    return setcookie($name, $value, $expires);
    }

But I get an error.

Parse error: syntax error, unexpected '(', expecting ')' in /var/www/running/8ima/lib/cookies.lib.php on line 38

How should I write it?

Answer

$expires = time()+604800

in the function definition.

Default value can't be the result of a function, only a simple value
QUoting from the manual:

The default value must be a constant expression, not (for example) a
variable, a class member or a function call.

Use:

public function set($name,$value,$expires = NULL) { 
    if (is_null($expires))
        $expires = time()+604800;
    echo $expires; 
    return setcookie($name, $value, $expires); 
}