> On Nov 28, 2016, at 7:22 PM, Dave Abrahams via swift-evolution
> <[email protected]> wrote:
>
>
> on Thu Nov 24 2016, Michael Ilseman <[email protected]> wrote:
>
>>> On Nov 17, 2016, at 2:54 AM, Tino Heth via swift-evolution
>> <[email protected]> wrote:
>>>
>>> An equivalent of "NS_REQUIRES_SUPER" (hopefully with a better name ;-) has
>>> been requested several
>> times, but never got the momentum it deserves.
>>> Considering the current confusion (especially in UIKit), it would be
>>> really nice to have some help from the compiler, and I wonder how
>>> composition and protocols would be helpful here at all.
>>>
>>
>> As an intermediary measure, this seems like an interesting QoI
>> improvement for the compiler: warn when super.foo() is not called in
>> the overridden method.
>
> Please no. Methods that need to be called when they are overridden are
> almost always a result of poor design.
>
> “I don't always do Object Oriented Programming, but when I do, I use
> the Template Method Pattern"
>
> understating-the-case-ly y'rs,
If you must enforce that a subclass override calls its super implementation,
you could enforce this via the type system, by creating a token type that only
the super implementation is able to construct:
open class Base {
public struct SuperFoo {
// Only the super implementation can create SuperFoos.
fileprivate init() {}
}
open func foo() -> SuperFoo {
doBaseStuff()
return SuperFoo()
}
}
// In another file...
class Derived: Base {
override func foo() -> SuperFoo {
// Must call super to get a SuperFoo that lets us out of the function
let result = super.foo()
doDerivedStuff()
return result
}
}
-Joe
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