Re: Swift enums and NSNotificationCenter
Re: Swift enums and NSNotificationCenter
- Subject: Re: Swift enums and NSNotificationCenter
- From: Rick Mann <email@hidden>
- Date: Thu, 06 Aug 2015 10:38:15 -0700
I guess. But we need some kind of extensible way of defining a set of valid selectors, ideally with optional string conformance and raw values (but not required to be strings).
Sent from my iPhone
> On Aug 6, 2015, at 09:20, Jens Alfke <email@hidden> wrote:
>
>
>> On 06 Aug 2015, at 02:19, Rick Mann <email@hidden> wrote:
>>> On Aug 5, 2015, at 17:14 , Jens Alfke <email@hidden> wrote:
>>> It’s part of the language design that only classes support inheritance, not structs or enums.
>>>
>>> Basically, subclassing pass-by-value types is problematic. For example, what happens when you assign a SubclassStruct value to a variable of type BaseStruct, or pass it to a function parameter of type BaseStruct? Do the extra instance variables get chopped off when it’s copied? What happens if you call a BaseStruct method that was overridden in SubclassStruct?
>>>
>>> C++ lets you do this, but it can lead to really nasty problems, so style guides like Effective C++ recommend avoiding it.
>>
>> But for extending the cases in an enum, it seems pretty nice.
>
> You can't do that, because instances of the subclassed enum won’t be valid instances of the super-enum.
>
> Consider enum A which has values x and y. Now subclass it as B and add a value z.
> What happens if you take a variable of type B with value z and assign it to a variable (or pass it to a parameter) of type A? Either you get an A with an illegal value, or you get a runtime exception. Yuck.
>
> —Jens
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