[swift-evolution] [swift-evolution-announce] [Review] SE-0089: Replace protocol<P1, P2> syntax with Any<P1, P2>

L Mihalkovic laurent.mihalkovic at gmail.com
Thu Jun 9 14:16:11 CDT 2016

> On Jun 9, 2016, at 6:49 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> on Wed Jun 08 2016, Jordan Rose <swift-evolution at swift.org> wrote:
>>> On Jun 8, 2016, at 13:16, Dave Abrahams via swift-evolution
>>> <swift-evolution at swift.org> wrote:
>>> on Wed Jun 08 2016, Thorsten Seitz
>>> <swift-evolution at swift.org
>>> <mailto:swift-evolution at swift.org>>
>>> wrote:
>>>> Ah, thanks, I forgot!  I still consider this a bug, though (will have
>>>> to read up again what the reasons are for that behavior).
>>> Yes, but in the case of the issue we're discussing, the choices are:
>>> 1. Omit from the existential's API any protocol requirements that depend
>>>  on Self or associated types, in which case it *can't* conform to
>>>  itself because it doesn't fulfill the requirements.
>>> 2. Erase type relationships and trap at runtime when they don't line up.
>>> Matthew has been arguing against #2, but you can't “fix the bug” without
>>> it.
>> #1 has been my preference for a while as well, at least as a starting
>> point. 
> I should point out that with the resyntaxing of existentials to
> Any<Protocols...>, the idea that Collection's existential doesn't
> conform to Collection becomes far less absurd than it was, so maybe this
> is not so bad.

the issue I have will all proposed Any<…> so far is that they are rather heavy, and in the case of a replacement for the obj-c   id<UITableViewDataSource> or worse MyTVC<UITableViewDataSource> (I know the example is absurd for it stands for a specific concrete type conforming), it involves a bit of magic. So played with a little toy syntax starting from the sugaring you are doing for literals:

Array<X>  —> [X]
Dict<X,Y> —> [X:Y]

stretching it to consider that existential are a degenerate form of literal notation, then the following would not look entirely out of place


[last example unfinished - missing opening syntax]

> -- 
> Dave
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