Star projection.md

Star projection

Requires a type cast.

Explanations

In Kotlin - Star projection is a combination of concepts in and out:

class MyGeneric<T : Any>(val data: T) {
    val state: T get() = data

    fun someStarProjection(myGeneric: MyGeneric<*>) {
        println("myGeneric: ${myGeneric}")
    }
}

fun starProjectionExample() {
    val myGeneric = MyGeneric(1)

    myGeneric.someStarProjection(myGeneric)
    myGeneric.someStarProjection(MyGeneric("11"))
}

In Objective-C we get this header:

__attribute__((objc_subclassing_restricted))
__attribute__((swift_name("MyGeneric")))
@interface SharedMyGeneric<T> : SharedBase
- (instancetype)initWithData:(T)data __attribute__((swift_name("init(data:)"))) __attribute__((objc_designated_initializer));
- (void)someStarProjectionMyGeneric:(SharedMyGeneric<id> *)myGeneric __attribute__((swift_name("someStarProjection(myGeneric:)")));
@property (readonly) T data __attribute__((swift_name("data")));
@property (readonly) T state __attribute__((swift_name("state")));
@end

On the Swift side we can use type casts:

private func starGenericProjecton() {
    let starProj = MyGeneric(data: NSNumber(12))
    
    starProj.someStarProjection(myGeneric: starProj as! MyGeneric<AnyObject>)
    starProj.someStarProjection(myGeneric: MyGeneric<AnyObject>(data: NSString("111")))
}

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