I've made a separate topic discussing the possible consequences of this change,
but I don't think the implications are really worth it. Parameter lists and
tuples are fundamentally similar, and that's why we're getting all of these
confusing edge cases.
Ultimately, this come down to two problems:
• Casting between functions of different labels is confusing. We've discussed
removing argument labels from function types for this reason. However, tuples
have this exact same problem. We should solve this generally, for tuples and
functions. A solution applicable to one is applicable to the other. If tuples
were only in the languages because they were meant to model a function's
arguments, I believe they still do in Swift 2.
Perhaps a tuple's argument labels should be in the name of it's containing
variable, like we plan for function types?
• Parameter lists have distinct annotations, which are unsuitable for full
exposure to the type system. However, I think this can be resolved through
something similar to the @noescape annotation, but for tuples, to restrict them
to ‘pure, nonescaping’ functional contexts (IE direct application to a
function).
For example:
apply<A, B>(in: @params A, function: A -> B) -> B {
return function(in)
}
//since we know the tuple cannot escape,
//only be passed to more functions with the exact parameter list represented by
A,
//we can safely use it with parameter decorations in a strictly functional
context:
apply(in: (&mutable, other), function: aFunction)
//or more practically:
(&mutable, other) => aFunction
Any return value is naturally escaping, meaning a returned tuple cannot have
modifiers such as @noescape and inout, since it can't provide that guarantee. I
think this addresses the problem much more directly.
There are inherently parallels between parameter lists and tuples, and that's
why functional programming languages rely on them. Swift actually has quite a
limited number of parameter list modifiers, so I think it's worth exploring
alternatives to fit these into the existing, much more generalised system,
before removing the parallel between parameter lists and tuples in favour of
something already known to be less flexible.
My review is inline.
> On 30 Jun 2016, at 19:26, Chris Lattner <[email protected]> wrote:
>
> Hello Swift community,
>
> The review of "SE-0111: Remove type system significance of function argument
> labels" begins now and runs through July 4. The proposal is available here:
>
>
> https://github.com/apple/swift-evolution/blob/master/proposals/0111-remove-arg-label-type-significance.md
>
> Reviews are an important part of the Swift evolution process. All reviews
> should be sent to the swift-evolution mailing list at
>
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
> or, if you would like to keep your feedback private, directly to the review
> manager.
>
> What goes into a review?
>
> The goal of the review process is to improve the proposal under review
> through constructive criticism and contribute to the direction of Swift. When
> writing your review, here are some questions you might want to answer in your
> review:
>
> * What is your evaluation of the proposal?
Strongly against, for the reasons described.
> * Is the problem being addressed significant enough to warrant a change to
> Swift?
Yes, but we should explore the alternatives.
> * Does this proposal fit well with the feel and direction of Swift?
Absolutely not, we will lose fundamental to Swift something by making this
change. We've already seen it by ‘removing’ tuple splat, and finding it to be
only surface-level. This is something already deeply ingrained in the type
system, and which provides a good deal of flexibility to functional code. The
addition of Never in favour of @noreturn shows how powerful the type system can
be, and I don't think we should walk this path half-heartedly.
> * If you have used other languages or libraries with a similar feature,
> how do you feel that this proposal compares to those?
I got started programming back in Objective-C, but most of my programming
experience is with Swift. In the various other (admittedly older) imperative
languages I've tried, I have been disappointed by the inflexibility of things
such as:
• Lack of tuple support, for straightforward return of >1 value where a formal
type is overkill.
• Lack of explicit optionals, or tacked-on optional support which interacts
poorly with generics and existing libraries.
• Lack of equal support for value-types, to varying degrees.
• Generics aren't actually generic, often requiring overloads for value-types,
due to their ‘defaulting’ behaviour.
The one thing these all have in common is the type system. There seems to be
real progress to be made by generalizing the type system as Swift has, so far.
Swift's functional generics system is incredible, largely thanks to the
modelling of parameter lists as a type, namely tuples. While this model has
fallen behind language advances, I think it can and should be brought up to
speed.
> * How much effort did you put into your review? A glance, a quick reading,
> or an in-depth study?
>
A lot of thought, while working with Swift and other languages.
Thanks for reading.
> More information about the Swift evolution process is available at
>
> https://github.com/apple/swift-evolution/blob/master/process.md
>
> Thank you,
>
> -Chris Lattner
> Review Manager
>
>
> _______________________________________________
> swift-evolution-announce mailing list
> [email protected]
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