> On 5 Sep 2016, at 13:29, Quincey Morris <quinceymor...@rivergatesoftware.com>
> wrote:
>
> On Sep 4, 2016, at 22:50 , Gerriet M. Denkmann <gerr...@mdenkmann.de> 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.
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