> On 29. Oct 2017, at 21:34, Chris Lattner <clatt...@nondot.org> wrote:
>
> // Magic, allows “overloaded/sugared postfix ()”.
> protocol CustomCallable {
> func call( …)
> }
>
> The only tricky thing about this is the call part of things. At least in the
> case of python, we want something like this:
>
> foo.bar(1, 2, a: x, b: y)
>
> to turn into:
> foo.dynamicMemberLookup(“bar”).call(1, 2, kwargs: [“a”:x, “b”:y])
>
> We don’t want this to be a memberlookup of a value that has “bar” as a
> basename and “a:” and “b:” as parameter labels.
I don't know much about Swift internals, but since you can already access a
function member without calling it, the parsing part of this sounds like it
would be straightforward.
If CustomCallable looked something like this:
protocol CustomCallable {
associatedtype Parameter
associatedtype Result
func call(_ parameterList: [(label: String?, value: Parameter)]) -> Result
}
implementations could decide how they want to handle named/unnamed parameters
etc themselves.
This approach would currently come with some limitations though: No throwing
(this could be addressed by a separate CustomThrowingCallable protocol), and –
since currently non-nominal types can't adopt protocols – an implementation of
CustomCallable could not accept, for example, both normal values and
closures/tuples.
>> Are there other uses for such a thing?
DynamicMemberLookupable could enable libraries dealing with key-value data,
like SwiftyJSON for example, to let users write myJson.someKey.nested instead
of myJson["someKey"]["nested"]. I'm sure there are more uses like this that are
not integrations with other languages.
— Lukas
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