CODEWITHSUNDEEP
iosobjective-ciphoneswiftgenerics
anuj
anuj

Reputation: 1060

In objective-c generics can i pass the type from 1 class to another

example of what I want to do is

@interface A<ObjectType> : NSObject
@end
@interface B<ObjectType> : NSObject
- (void)doSomething:(ObjectType)obj;
@end
@implementation B
- (void)doSomething:(id)obj {
   **A<ObjectType> *a = [[A alloc] init];**
   [a addObject:obj];
}
@end

Basically I want A to be allocated with the same type as B was allocated with.

The line within ** won't compile. What is the right syntax to do something like this?

Upvotes: 0

Views: 1941

Answers (2)

CRD
CRD

Reputation: 53000

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 doSomething: method.

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

Upvotes: 4

Ethan
Ethan

Reputation: 471

is this ok for you?

@protocol ObjectType <NSObject>

- (void)addObject:(id)obj;


@end

@interface A : NSObject <ObjectType>


@end

@implementation A

- (void)addObject:(id)obj {

}

@end
@interface B : NSObject <ObjectType>


- (void)doSomething:(id<ObjectType>)obj;
@end
@implementation B

- (void)addObject:(id)obj {

}

- (void)doSomething:(id)obj {
    id<ObjectType> a = [[A alloc] init];
    [a addObject:obj];
}

@end

Upvotes: -1

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