Re: Init in Swift
Re: Init in Swift
- Subject: Re: Init in Swift
- From: "Gerriet M. Denkmann" <email@hidden>
- Date: Wed, 07 Sep 2016 07:17:31 +0700
> On 5 Sep 2016, at 13:29, Quincey Morris <email@hidden> wrote:
>
> On Sep 4, 2016, at 22:50 , Gerriet M. Denkmann <email@hidden> wrote:
>
> If you can’t do that, you can do it with a closure, assuming the places of definition aren’t more complicated than in your code. Something like this:
>
>> class SuperClass
>> {
>> let knownBySuperclass: Int
>> let onlyKnownBySubclass: Int
>>
>> init(some: Int, calc: (known: Int) -> Int)
>> {
>> knownBySuperclass = some * 2
>> onlyKnownBySubclass = calc (known: knownBySuperclass)
>> }
>>
>> final func someFunction() -> Void
>> {
>> print("Should never be zero: \(onlyKnownBySubclass)")
>> }
>> }
>>
>> final class SubClass: SuperClass
>> {
var localConstantDependingOnSuper: Int // should really be a constant
>> init(some: Int)
>> {
localConstantDependingOnSuper = 0 // all must be set before calling super
>> super.init(some: some) { $0 + 5 }
localConstantDependingOnSuper = knownBySuperclass + 27
>
>> }
>> }
>>
>> let a = SubClass(some:11)
>> a.someFunction() // prints: “Should never be zero: 27”
This trick with the closure is rather neat. I would never have come up with it. Thanks for telling me!
But what to do about localConstantDependingOnSuper?
> More globally, this sort of thing is not terribly idiomatic for Swift, because you’re trying to hide things that could get exposed other ways, for example, by “hostile” subclassing. The Swift-ier way would be to use a protocol instead of (or in addition to, but preferably instead of) the superclass. The protocol would “force” the subclass to define its own “onlyKnownBySubclass” locally.
I do not think this would work for me. There are several subclasses and the superclass contains lots of functions (some of which are overwritten by subclasses).
If the superclass becomes a protocol then all this code had to be duplicated in each subclass.
Another problem:
Super → SubA and SubB.
SubA → SubA1 and SubA2
SubB → SubB1 and SubB2
Both SubA1 and SubB1 have identical functions. As have SubA2 and SubB2.
Multiple inheritance would be a solution here; but neither Objective-C nor Swift can do this (and I don’t like C++).
Current solution: cut and paste and trying to keep both versions in sync.
Anything better?
Kind regards,
Gerriet.
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden