[swift-evolution] [Proposal] Explicit Synthetic Behaviour

Xiaodi Wu xiaodi.wu at gmail.com
Tue Sep 12 23:28:20 CDT 2017

On Tue, Sep 12, 2017 at 23:26 Gwendal Roué <gwendal.roue at gmail.com> wrote:

> > Le 13 sept. 2017 à 04:05, Xiaodi Wu <xiaodi.wu at gmail.com> a écrit :
> >
> > On Tue, Sep 12, 2017 at 2:30 PM, Gwendal Roué <gwendal.roue at gmail.com>
> wrote:
> > >> In none of those cases, the compiler emits any warning. It's thus
> easy to forget or miss the problem, and uneasy to fix it (you'll need a
> runtime failure to spot it, or a thorough code review).
> > >>
> > >> I hope you agree with this last sentence. This unbalance between the
> easiness of the mistake and the easiness of the fix should ring a bell to
> language designers.
> > >
> > > Suppose instead this were about a protocol named Fooable and a
> requirement called foo() that has a default implementation. Everything you
> just talked about would apply equally. Am I to understand that you are
> opposed to default implementations in general? If so, then that’s got
> nothing to do with synthesized Equatable conformance. If not, then you’ll
> have to justify why.
> >
> > Sounds like a good argument, until one realises that if a protocol does
> not provide a default implementations for a method, it may be because a
> default implementations is impossible to provide (the most usual case), or
> because it would be unwise to do so.
> >
> > And indeed, the topic currently discussed is not if we should remove or
> not default implementations. Instead, the question is: is it wise or not to
> provide an *implicit* default Equatable/Hashable/XXX implementation?
> >
> > Right, _that_ is the question. It was asked during review for the
> proposal, and the agreed upon answer is _yes_.
> Wrong. This whole thread is about *explicit* synthetic behavior;. If an
> agreed proposal has to be invalidated in the way, _so be it_.
> Gwendal

Explicit (e.g., "AutoEquatable") and implicit synthetic behavior were both
considered during the proposal which approved the implicit behavior. This
question has been asked and answered.
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