How can I find out the Objective-C generics type?

Question

Xcode 7 contains an Objective-C variant, where you can define a type-hint for (homogenous) NSArray return values and properties, defined such as NSArray<UIImage*>.

I'd like to use this feature to rewrite my JSON-deserializer class (which needs such kind of type hints – previously I have solved this by adding a -(Class)jsonHintForKey:(NSString*)key to my classes that have homogenous arrays as properties.)

Do you know whether (and if so, how) I can use the Objective-C runtime to get the class of this new type hint at runtime?

Answer 1

The lightweight generics introduced in Xcode 7 are just compile time hints to help the compiler raise warnings, but at run time you get the same old behavior with your variable being just NSArrays of ids.

Source: WWDC '15 "Swift and Objective-C Interoperability" session

See the transcript of the talk:

So the entire lightweight generics feature is based on a type erasure model. Which means that the compiler has all of this rich static type information but it erases that information when generating code.

Answer 2

It is not possible to do that.

Generics were introduced in objective-c to improve the bridge between swift and objective-c. The advantage it gives to objective-c is only useful at compile time, and I that information is lost at runtime.