The example in this chapter puts the block declaration, assignment, and usage on three separate lines of code for readability.

When you need to pass an integer into a method, such as NSNumber’s numberWithInt:, you can pass the int anonymously:

/​/​ ​O​p​t​i​o​n​ ​1​:​ ​T​o​t​a​l​l​y​ ​b​r​e​a​k​ ​i​t​ ​d​o​w​n​
i​n​t​ ​i​;​
i​ ​=​ ​5​;​
N​S​N​u​m​b​e​r​ ​*​n​u​m​ ​=​ ​[​N​S​N​u​m​b​e​r​ ​n​u​m​b​e​r​W​i​t​h​I​n​t​:​i​]​;​

/​/​ ​O​p​t​i​o​n​ ​2​:​ ​S​k​i​p​ ​t​h​e​ ​v​a​r​i​a​b​l​e​ ​d​e​c​l​a​r​a​t​i​o​n​
N​S​N​u​m​b​e​r​ ​*​n​u​m​ ​=​ ​[​N​S​N​u​m​b​e​r​ ​n​u​m​b​e​r​W​i​t​h​I​n​t​:​5​]​;​

Because blocks are variables, you can do this with blocks as well. In fact, this is the most common way to use blocks. You will rarely declare a block variable so that you can pass the block into methods; you’ll usually use them anonymously.

Modify the exercise in this chapter to pass the block anonymously as an argument to enumerateObjectsUsingBlock:. That is, keep the block, but get rid of the block variable.

In Chapter 24, you used NSNotificationCenter’s addObserver:selector:name:object: method to register to receive callbacks via your zoneChange: method. Update that exercise to use the addObserverForName:object:queue:usingBlock: method instead. Look up its details in the developer documentation.

This method takes a block as an argument and then executes the block instead of calling back to your object when the specified notification is posted. This means that your zoneChange: method will never be called. The code inside this method will instead be in the block.

The passed-in block should take a single argument (an NSNotification *) and return nothing, just as the zoneChange: method does.

You can pass nil as the argument for queue:; this argument is used for concurrency, a topic we won’t cover in this book.