Friday, July 31, 2015

Objective-C Improvements and Swift Interoperability

WWDC 2015 Session 401 (video, PDF):

Go to any Objective-C header and choose the ‘show related items’ button in the top-left corner. This will bring down a menu of related items, one of which is ‘generated interface.’ And this will show you the Swift mapping for that header. This is the exact same view that you got in Xcode 6 using the ‘jump to definition’ feature, but now you can get it easily from any header in your target.


Now, on both of these examples, I have shown that these methods in Objective-C have multiple parameters, only one of which is the error parameter, but there are also cases where methods only have one parameter and you will get something like ‘check resource is researchable and return error.’ As you can see in Swift, since we already know that the method can return an error from that ‘throws’ keyword, we will chop off those last three words for you, just for you!

I guess that answers my question.

Jordan Morgan:

The first step to making this better is one of my favorite new Objective-C features, nullability annotations.


Though it took about thirty-two years, generics is now a thing in Objective-C.


Essentially, we’ve informed the compiler that the property and its collection will have some kind of a UIView. This allows for more information in the type contract that we’ve not had before.

The real treat? Implicit downcasting.


There’s a couple of this going on here. Firstly you will notice that we are not using ObjectType anywhere. It appears that the name of a Generic reference is only usable in the header of a class. I’ve tried all sorts of syntaxes to see if there was a way to declare and use it in the implementation, but I’ve been unsuccessful. So I’ve concluded that Objective-C Generics simply don’t make the placeholders available to implementations. Unfortunately I cannot confirm against Apples code.

What I have concluded is that when a Generic is resolved by the compiler, it resolves to the top most class that can replace it. Normally this is id, however bounded Generics can make this more specific. See Restricting Generics below.

Joe Groff:

ObjC generics also can’t be part of the canonical type system without breaking C++ templates

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