A compound statement enclosed in parentheses may appear as an expression in GNU C.
此用法來自gcc官方說明，源自gcc對c的擴展，如今被clang繼承。

({ int y = foo (); int z;
   if (y > 0) z = y;
   else z = - y;
   z; })

在iOS中可以這樣使用：

    UIButton *pop = ({
        UIButton *button = [[UIButton alloc] initWithFrame: CGRectMake(160, 400, 120, 40)];
        button.backgroundColor = [UIColor redColor];
        [button setTitle: @"pop" forState: UIControlStateNormal];
        [button addTarget: self action: @selector(popView) forControlEvents: UIControlEventTouchUpInside];
        button;
    });

有點像block和內聯(lián)函數(shù)的結合體，它最大的意義在于將代碼整理分塊，將同一個邏輯層級的代碼包在一起。

值的注意的是： 返回值和代碼塊結束點必須在結尾