Block对象

我不知道该如何翻译Block这个关键字在Objective-C中，但是可以肯定得是：Block是一段代码。

我们来看它的英文解释:

Blocks are a way to define a block of code that you will use at a later time.

Sometimes people refer to blocks as anonymous functions because they are functions that aren’t
attached to an entity.

事实上，Block有点类似我们C#或者Java里的匿名函数。

来看个例子： 

eg:

squareThis = ^(float x){
　　return x * x;
};

float result = squareThis(4);
NSLog(@"result = %f", result);

This will print out the following output to the console log:
result = 16.000000

NSString *title = @"Multiply Block Execution";
float (^multiplyThese)(float, float) = ^(float x, float y)
{
    NSLog(title);

    return x * y;
};

NSLog(@"multiplyThese(3,4) = %f", multiplyThese(3,4));

Output:

Multiply Block Execution
multiplyThese(3,4) = 12.000000