roleassignment member is a group or user --check

Hi ,

I am using client object model

I want to check a roleassignment member is a group or an user ?

I am using the below code...its not working

 if (roleAssignment.Member is Group)
                    {
                        var group = (Group)roleAssignment.Member;
//do something
            }
    else if (roleAssignment.Member is User)
                    {
                        var user = (User)roleAssignment.Member;
//do something

}

Like Cricket