GenericArrayExtension.playground

protocol AProtocol {}

protocol ABProtocol: AProtocol {}

struct ABStruct: ABProtocol {}

struct Wrapper<T> {
    let object: T
}

extension Array where Element == Wrapper<AProtocol> {
    func merge(with otherArray: [Element]) {}
}

let wrapper1: Wrapper<ABProtocol> = Wrapper(object: ABStruct())
let wrapper2: Wrapper<ABProtocol> = Wrapper(object: ABStruct())
let wrappers1 = [wrapper1, wrapper2]
let wrappers2 = [wrapper2, wrapper1]
// Following produces compilation error:
// '[Wrapper<ABProtocol>]' is not convertible to 'Array<Wrapper<AProtocol>>'
let result = wrappers1.merge(to: wrappers2)