[swift-evolution] Static Dispatch Pitfalls

Matthew Johnson matthew at anandabits.com
Fri May 20 13:04:45 CDT 2016

> On May 20, 2016, at 12:35 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
>> On May 20, 2016, at 9:17 AM, Austin Zheng <austinzheng at gmail.com> wrote:
>> I almost want to propose forbidding methods in protocol extensions unless they're also a requirement in the protocol itself, but I don't think that would fly.
> I don’t think that would fly :-).  That said, has anyone considered requiring a keyword on the method in the protocol extension that makes it explicit that the dispatch is non-dynamic?

I believe `final` has been discussed previously for this purpose.  IIRC the intent was to *disallow* the type to have its own method with the same signature.  However, that interacts poorly with retroactive conformance which means `final` is probably not best choice.

Before we introduce a keyword I think we should be sure the current semantics are what we plan to stick with.  I haven’t seen any good alternatives proposed, but people do keep bringing up this topic.  The desire is usually to change the semantics, not just clarify the existing semantics.

> -Chris
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