Why you should use instancetype instead of id

In my previous entry, I discussed when id will be promoted to instancetype. But now that I’ve explained this, I’d like to explain why you should understand this but not rely on it. Instead, you should use instancetype directly.

Let me start with this bold statement, then I’ll back up and explain it: Use instancetype whenever it’s appropriate, which is whenever a class returns an instance of that same class.

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When is id promoted to instancetype?

instancetype is a special type that can be returned from an Objective-C method. It specifies that the return is an object of the same type as the receiving class. In some cases, the compiler promotes an id return to an instancetype: For instance, despite the definition of [[NSString alloc] init], the compiler knows that it returns an NSString.

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Objective-C property proposal: mainthreadonly

I’d like to propose a new language feature for Objective-C, a property attribute that would indicate that a property should only be set from the main thread.

Let me be clear: Objective-C does not do this. But wouldn’t it be cool if it did?

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Trimming a level of indent with @synchronized and @autoreleasepool

I haven’t seen this discussed anywhere, but you can eliminate a level of indentation when using @synchronized and @autoreleasepool blocks in a loop or conditionally. This falls naturally as a result of the way the C language works, and how these blocks work, but it took me a while to realize it.

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Reachability

Apple has a sample code package called Reachability. It wraps an iOS framework called SystemConfiguration, and can be used to determine network status, and catch events about networking going up and down. In the past, it’s been an ugly chunk of sample code, but it’s pretty respectable now.

One thing Reachability is not, however, is a crystal ball. Please don’t use it as if it were.

In this article, I’m going to discuss how to use it. Because this is one thing I see a lot of developers get wrong.

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