ObjC 中括号和花括号括起来的几个语句的赋值 [英] Assignment of several statements enclosed in parentheses and curly braces in ObjC

问题描述

我正在仔细阅读第三方 RESideMenu 框架的代码，并注意到一些奇怪的语法，但似乎工作得很好.这是令人困惑的一点:

I was perusing the code of the third-party RESideMenu framework, and noticed some strange syntax that seemed to work just fine. Here is the confusing bit:

self.tableView = ({
    UITableView *tableView = [[UITableView alloc] initWithFrame:frame style:UITableViewStylePlain];
    tableView.autoresizingMask = mask;
    tableView.delegate = self;
    tableView.dataSource = self;
    tableView.opaque = NO;
    tableView.backgroundColor = [UIColor clearColor];
    tableView.backgroundView = nil;
    tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
    tableView.bounces = NO;
    tableView.scrollsToTop = NO;
    tableView;
});

这个语法是如何工作的?我怀疑它与 C 级块作用域有关，但我以前从未见过这种情况.我也认为这可能是 Objc-2.0 文字的一个新特性，但我认为这不是真的.

How does this syntax work? I suspect it has something to do with a C-level block scoping, but I have never seen this before. I also considered it may be a new feature with Objc-2.0 literals, but I don't think that is true.

所以我想我的问题是它是如何工作的/是什么使它起作用?

So I guess my question is how does this work/what makes this work?

推荐答案

如 NSHipster:

神奇的背后是一个 GCC C 扩展，如果用方括号和圆括号括起来，它会导致代码块返回一个值.

Behind the magic is a GCC C extension, which causes a code block to return a value if enclosed within brackets and parentheses.

这不仅将配置细节隔离到初始化中，而且额外的作用域允许在后续初始化中重用框架、按钮和视图等通用变量名称.不再需要 loginButtonFrame = .../signupButtonFrame = ...!

This not only segregates configuration details into initialization, but the additional scope allows generic variable names like frame, button, and view to be reused in subsequent initializations. No more loginButtonFrame = ... / signupButtonFrame = ...!

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