objective-c - 类型之间而不是变量之间的插入符，用括号括起来

Question

我在浏览 Apple 的文档时看到了类似这样的内容 (void (^)(void))。有人能解释一下这句话的意思吗？ ^ 是异或，对吧？ void XOR void 对我来说没有多大意义？

还有类似 (void (^)(BOOL finish))

Answer 1

这些是向 Objective-C 添加匿名函数和函数对象的 block 。参见例如Introducing Blocks and Grand Central Dispatch :

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:

• Blocks can be defined inline, as “anonymous functions.”
• Blocks capture read-only copies of local variables, similar to “closures” in other languages

声明 block 变量:

void (^my_block)(void);

为其分配一个 block 对象:

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

调用它:

my_block(); // prints “hello world\n”

接受 block 作为参数:

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

将该方法与内联 block 一起使用:

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