ObjC特殊赋值方式

偶然今天碰到的赋值方式 暂时不知道怎么称呼，标记下

self.awesometransition.containerBackgroundView = ({
    UIView *bgView = (UIView *)[[[NSBundle mainBundle] loadNibNamed:@"ContainerBackgroundView" owner:nil options:nil] lastObject];
    bgView;
});