How can I find out the Objective-C generics type?
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
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.
Generic Type In Objective C
id is in Objective-C, a untyped Objective-C object pointer.
id test = [[NSMutableArray alloc] init];
How can I create a generic property in Objective-C?
Here is answer.
@interface myParentView< T: parentModel*> :UIView
@property T myObject; // myObject is object of parentModel
In all subclass:
@interface myChildViewOne :myParentView<childModel>
// Now myObject is object of childModel
Obj C has complicated syntax, But we can achieve generic property like above.
lightweight generics in objective c
Objective-C generics really are lightweight, and were added to improve interoperability with Swift, not to make Objective-C code safer. Similar to nullability, think of generics as a way to annotate your interface rather than a reason to change your implementation.
id in the implementation is the best way forward.
Further reading: article on Objective C Generics. Read bob’s comment on that article if you want to know about
Using a generic Swift class in Objective-C
Swift generic types cannot be used in Objective-C.
This excludes Swift-only features such as those listed here:
In objective-c generics can i pass the type from 1 class to another
Objective-C does not have generics, Apple introduced something they term Lightweight Generics, and you may read the "lightweight" as "faux".
Here is Apple's own statement on what they do:
Allow you to specify type information for collection classes such as NSArray, NSSet, and NSDictionary. The type information improves Swift access when you bridge from Objective-C and simplifies the code you have to write.
Notice the "improves Swift access" and the lack of "improves Objective-C". These lightweight generics are essentially annotations for the Swift compiler when it is importing Objective-C types. On the Objective-C side maintaining the generic invariants is largely the responsibility of the programmer.
You can use the lightweight generic annotations (a) in an
@interface and (b) when declaring a variable whose type has lightweight generic annotations. You cannot otherwise use the annotations, in particular you do not use them in an
@implementation other than (b) above. Within the
@implementation for a lightweight generic annotated
@interface rather than use the "type parameters" from the annotations you use the
id type - as you have done with your
The latest Xcode/Clang will provide some checking of lightweight generic annotations in Objective-C, but it is limited and should in no way be taken as a guarantee that the generic conditions are being checked.
In summary, unless you are planning to interwork with Swift using the lightweight generic annotations in Objective-C is of little benefit, and it certainly does not give you "generics" in the usual sense (i.e. parametric generic types).
Undoubtedly not what you wanted to hear, but HTH
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