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本文链接：https://blog.youkuaiyun.com/zheng3stone/article/details/53185656

本文介绍了Objective-C中带参数和返回值的Block的定义与使用。Block可以像方法和函数一样接收参数并返回值，示例展示了如何声明一个接受两个double类型参数并返回它们乘积的Block。

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今天讲Objective-C中带参数和返回值的Block。

下面是ios reference官方的讲解：

Blocks Take Arguments and Return Values

Blocks can also take arguments and return values just like methods and functions.

As an example, consider a variable to refer to a block that returns the result of multiplying two values:

double (^multiplyTwoValues)(double, double);

The corresponding block literal might look like this:

^ (double firstValue, double secondValue) {
	return firstValue * secondValue;
}

The firstValue and secondValue are used to refer to the values supplied when the block is invoked, just like any function definition. In this example, the return type is inferred from the return statement inside the block.

If you prefer, you can make the return type explicit by specifying it between the caret and the argument list:

^ double (double firstValue, double secondValue) {
	return firstValue * secondValue;
}

Once you’ve declared and defined the block, you can invoke it just like you would a function:

double (^multiplyTwoValues)(double, double) =
						  ^(double firstValue, double secondValue) {
							  return firstValue * secondValue;
						  };

double result = multiplyTwoValues(2,4);

NSLog(@"The result is %f", result);