类型之间的尖号字符，而不是变量，用括号括起来 [英] Caret character between types rather than variables, surrounded by parentheses

问题描述

我正在查看Apple的文档，并且看到了类似(void (^)(void))的内容.有人可以解释这句话的意思吗? ^是XOR，对吗? void XOR void对我来说没有多大意义?

I was going through Apple's documentation and I saw something like this (void (^)(void)). Can somebody explain what this statement means? ^ is XOR, right? void XOR void doesn't makes much sense to me?

还有类似(void (^)(BOOL finished))

推荐答案

这些是将匿名函数和函数对象添加到Objective-C的块.参见例如引入积木和盛大中央调度:

These are blocks which add anonymous functions and function objects to Objective-C. See e.g. Introducing Blocks and Grand Central Dispatch :

块对象(非正式地称为块")是C以及Objective-C和C ++的扩展，使程序员可以轻松地定义独立的工作单元.块与传统函数指针类似，但功能比传统函数指针强大得多.关键区别在于:

Block objects (informally, "blocks") are an extension to C, as well as Objective-C and C++, that make it easy for programmers to define self-contained units of work. Blocks are similar to — but far more powerful than — traditional function pointers. The key differences are:

• 块可以内联定义为匿名函数".
• 块捕获局部变量的只读副本，类似于其他语言中的"closures"

声明一个块变量:

void (^my_block)(void);

为其分配块对象:

my_block = ^(void){ printf("hello world\n"); };

调用:

my_block(); // prints "hello world\n"

接受块作为参数:

- (void)doSomething:(void (^)(void))block;

将该方法与内联块一起使用:

Using that method with an inline block:

[obj doSomeThing:^(void){ printf("block was called"); }];

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