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

问题描述

我正在浏览 Apple 的文档，我看到了类似这样的 (void (^)(void)).有人能解释一下这个说法是什么意思吗?^ 是异或，对吧?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

这些是向 Objective-C 添加匿名函数和函数对象的块.见例如介绍 Blocks 和 Grand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，它使程序员可以轻松定义自包含的工作单元.块类似于 - 但比 - 传统的函数指针强大得多.主要区别在于:

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:

• 块可以被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闭包"

声明一个块变量:

void (^my_block)(void);

为其分配一个块对象:

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

调用它:

my_block(); // prints "hello world
"

接受一个块作为参数:

- (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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