[swift-evolution] Casting Bug Swift

James Campbell james at supmenow.com
Thu Feb 25 11:30:47 CST 2016


In the actual code, the array with the protocol type i.e [Eatable] is used
as an associated type. So perhaps it normally gets rejected but isn't in
this case ?



*___________________________________*

*James⎥Head of Clown*

*james at supmenow.com <james at supmenow.com>⎥supmenow.com <http://supmenow.com>*

*Sup*

*Runway East *

*10 Finsbury Square*

*London*

* EC2A 1AF *

On Thu, Feb 25, 2016 at 5:07 PM, Jordan Rose <jordan_rose at apple.com> wrote:

> I think there are two things going on here:
>
> - The compiler allows a memory-corrupting cast, which should be rejected
> (a bug).
> - But it's a useful thing to do (a language change).
>
> I'm actually surprised about the bug, since we get plenty of questions
> about why the compiler doesn't allow it, implying that the compiler is
> indeed rejecting it. The answer is that protocol values and class values
> don't have the same representation, so converting between [Eatable] and
> [Burger] is an O(N) operation that requires allocating a new array. But
> that may not be a good enough reason not to allow it—conversions from
> NSArray to Array can do the same thing if the NSArray was mutable.
>
> Jordan
>
>
> On Feb 25, 2016, at 8:53 , Radosław Pietruszewski via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Hey James,
>
> The appropriate place for compiler bugs is https://bugs.swift.org, not
> Swift Evolution.
>
> Best,
> — Radek
>
> On 25 Feb 2016, at 17:44, James Campbell via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Say I have been passed an array of objects that conform to a protocol
> called "Eatable" i.e [Eatable]
>
> If I then try to cast them to an array of classes who happen to implement
> that protocol i.e [Burger]
>
> The compiler lets me but in the runtime it corrupts the memory.
>
> *___________________________________*
>
> *James⎥iOS Lead*
>
> *james at supmenow.com <james at supmenow.com>⎥supmenow.com
> <http://supmenow.com/>*
>
> *Sup*
>
> *Runway East *
>
> *10 Finsbury Square*
>
> *London*
>
> * EC2A 1AF *
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160225/9ce789e4/attachment.html>


More information about the swift-evolution mailing list