kvo-user.m

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"currentUser"]) {
        if (self.currentUser) {
            [self hopTo:@"main" then:nil];
        }
        else {
            [self hopTo:@"signup_login" then:nil];
        }
    }
    
    // ...
}