> On Nov 28, 2017, at 8:57 PM, Slava Pestov <spes...@apple.com> wrote:
>
> Hi Chris,
>
>> On Nov 28, 2017, at 8:54 PM, Chris Lattner via swift-evolution
>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
>>
>> “post.author" always invokes the DynamicMemberLookupProtocol proposal.
>> “post.author()” would invoke the “DynamicCallableWithKeywordsToo” hook in
>> the dynamic callable proposal:
>> https://gist.github.com/lattner/a6257f425f55fe39fd6ac7a2354d693d
>> <https://gist.github.com/lattner/a6257f425f55fe39fd6ac7a2354d693d>
> Elsewhere in Swift, it is generally the case that
>
> foo.bar()
>
> is equivalent to
>
> let fn = foo.bar
> fn()
That’s not actually the generally the case once you include some keyword
arguments in the call. Recall that function types don’t have keyword argument
labels any longer, so:
foo.bar(x: 42)
Is not equivalent to:
let fn = foo.bar
fn(x: 42)
> Would this equivalence still hold with your proposal(s)?
It completely depends on the direction of the DynamicCallable proposal:
https://gist.github.com/lattner/a6257f425f55fe39fd6ac7a2354d693d
<https://gist.github.com/lattner/a6257f425f55fe39fd6ac7a2354d693d>
In my original proposal, I had no hook for “DynamicCallableWithKeywordsToo”.
Feedback from the list was that people care about smalltalk derived languages
(Ruby, Squeak, and yes, ObjC/Swift) and so I added this as a generalization.
That said, I’m not attached to it at all. I can see the advantages of
supporting these forms, but I can also see the concern that you’re observing.
I think that proponents for “DynamicCallableWithKeywordsToo” would say that
Smalltalky languages (including Swift per the example above) do not provide the
ability to separate out the base name, and those a bridge to those language can
justifiably eject this concern. In contrast, since Python *does* allow the
substitution that you’re suggesting, its bridge absolutely would provide that
capability.
In the end, it comes down to the cost benefit tradeoff we’ll have to weigh: how
much generality and power is needed and can be justified?
-Chris
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