> Am 11.06.2016 um 15:08 schrieb L. Mihalkovic <laurent.mihalko...@gmail.com>:
>
>
>> On Jun 11, 2016, at 2:05 PM, Thorsten Seitz <tseit...@icloud.com> wrote:
>>
>>
>>> Am 11.06.2016 um 12:38 schrieb L. Mihalkovic <laurent.mihalko...@gmail.com>:
>>>
>>>
>>>> On Jun 11, 2016, at 11:30 AM, Thorsten Seitz <tseit...@icloud.com> wrote:
>>>>
>>>>
>>>>> Am 11.06.2016 um 08:00 schrieb L. Mihalkovic
>>>>> <laurent.mihalko...@gmail.com>:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Regards
>>>>> (From mobile)
>>>>>> On Jun 10, 2016, at 9:35 PM, Thorsten Seitz via swift-evolution
>>>>>> <swift-evolution@swift.org> wrote:
>>>>>>
>>>>>>
>>>>>>> Am 09.06.2016 um 19:50 schrieb Thorsten Seitz via swift-evolution
>>>>>>> <swift-evolution@swift.org>:
>>>>>>>
>>>>>>>
>>>>>>>> Am 09.06.2016 um 18:49 schrieb Dave Abrahams via swift-evolution
>>>>>>>> <swift-evolution@swift.org>:
>>>>>>>>
>>>>>>>>
>>>>>>>> on Wed Jun 08 2016, Jordan Rose <swift-evolution@swift.org> wrote:
>>>>>>>>
>>>>>>>>>> On Jun 8, 2016, at 13:16, Dave Abrahams via swift-evolution
>>>>>>>>>> <swift-evolution@swift.org> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> on Wed Jun 08 2016, Thorsten Seitz
>>>>>>>>>
>>>>>>>>>> <swift-evolution@swift.org
>>>>>>>>>> <mailto:swift-evolution@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.
>>>>>>>
>>>>>>> I think the problem is more that Any<Collection> does not conform to a
>>>>>>> specific value for a type parameter T: Collection
>>>>>>>
>>>>>>> What I mean by this is that `Collection` denotes a type family, a
>>>>>>> generic parameter `T: Collection` denotes a specific (though unknown)
>>>>>>> member of that type family and `Any<Collection>` denotes the type
>>>>>>> family again, so there is really no point in writing Any<Collection>
>>>>>>> IMO.
>>>>>>> The type family cannot conform to T because T is just one fixed member
>>>>>>> of it.
>>>>>>> It conforms to itself, though, as I can write
>>>>>>> let c1: Any<Collection> = …
>>>>>>> let c2: Any<Collection> = c1
>>>>>>>
>>>>>>> That’s why I think that we could just drop Any<Collection> and simply
>>>>>>> write Collection.
>>>>>>
>>>>>>
>>>>>> Let me expand that a bit:
>>>>>>
>>>>>> Actually all this talk about existentials vs. generics or protocols vs.
>>>>>> classes has had me confused somewhat and I think there are still some
>>>>>> misconceptions present on this list sometimes, so I’ll try to clear them
>>>>>> up:
>>>>>>
>>>>>> (1) misconception: protocols with associated types are somehow very
>>>>>> different from generics
>>>>>>
>>>>>> I don’t think they are and I will explain why. The only difference is
>>>>>> the way the type parameters are bound: generics use explicit parameter
>>>>>> lists whereas protocols use inheritance. That has some advantages (think
>>>>>> long parameter lists of generics) and some disadvantages.
>>>>>> These ways are dual in a notation sense: generic types have to have all
>>>>>> parameters bound whereas protocols cannot bind any of them.
>>>>>> The „existential“ notation `Any<>` being discussed on this list is
>>>>>> nothing more than adding the ability to protocols to bind the parameters
>>>>>> to be used just like Java’s wildcards are adding the opposite feature to
>>>>>> generics, namely not having to bind all parameters.
>>>>>
>>>>> btw, i tried to to see if Any<> could have a simpler alternative
>>>>> https://gist.github.com/lmihalkovic/8aa66542f5cc4592e967bade260477ef
>>>>
>>>> As you know I like using `&` as type intersection operator. But you write
>>>> "The syntax leave a void when it comes to expressing the so called Top
>>>> type:“
>>>> Why? Just give the top type a name, e.g. `Any` and you are done.
>>> Yes.. I just don't like magic. I think that all types should be expressable
>>> with a syntax and that you can then decide to alias one parsing case with a
>>> specific name. Not the other way around.
>>
>> Well, I think that would be backwards, because we have a nominal type
>> system. That means that the syntax for a type is just its name.
>
> I realize we do not understand each other.
> The words we use now to describe a behavior are just that, words. As is the
> concepts they describe are useless to the computer running the compiler.
> So we need to map these concepts into a heuristic that a fast but dumb
> computer will be able to reason with. The code to do that will be either
> clean and organized, or it will look contrived and full of different paths
> that will be difficult to mesh together. Of all the possible ways in which
> swift can behave as a language, some will lead to the former, others to the
> latter code. I think this is not fate or something you find out after the
> decision was made and you struggle to carry it through. This is something
> that can partially be predicted. One of the tools for such prediction is to
> translate the concepts into a grammar that will show formalize the logic. The
> simpler the logic, the cleaner (not simple) the final code.
>
> Saying that the syntax for a type is a name is of no use whatsoever for the
> compiler implementer. It is so universally true that it cannot help in any
> way whatsoever decide the shape of the swift grammar, much less the structure
> of the c++ code implementing it.
>
>> `&` is a type operator which creates a new type from its operands.
>> `where` clauses add constraints to types.
>> But it all starts with a type's name.
>>
>> The only magic would be that all type definitions (`protocol` etc.) which do
>> not give a supertype they conform to, will implicitly conform to `Any`, i.e.
>
> I call magic the core notions of swift that cannot be expressed in swift but
> have to parachutted in by the compiler. If you read Chris' initial message
> you will see that he said as much, that adopting P&Q as syntax was leaving a
> gap that the compiler would have to magically fill.
>
>
>>
>> protocol Foo { … }
>>
>> means
>>
>> protocol Foo : Any { … }
>>
>> That’s less magic than creating a special syntax just to express the top
>> type.
>
> I will try again... Would it be easier to understand it if instead of magic I
> said arbitrary? You are creating a special case: you decide arbitrarily that
> the special series of characters 'A' 'n' 'y' with this precise casing and
> without any spaces is going to be adorned with a special meaning when used in
> specific situations. This is not something you deduced. My approach is
> exactly the opposite: _[] does not describe the top type because I have a
> special affinity with these characters, it describes the top type because it
> is the only possible logical conclusion from having followed a set of rules
> attached to a syntax that describes ALL existentials. And because it is not
> particularly savory, I typealias it to something else. But this is not in the
> compiler, it us in the standard linrary... inside swift, not outside.
Ok, that's a good argument. But your proposal does not contain those rules.
Why should _[] describe the top type? You just say this in your proposal, but
you do not define rules what _[] means.
_[A,B] describes the type intersection of A and B, i.e. it contains all members
of A which are also members of B. _[] does not list any types, so one might
conclude that it has no members and therefore must be the bottom type!
Or _[A,B] in reality means _[A,B,Any], i.e. A & B & Any which of course is
equal to A & B. Then _[] would just mean Any, but we would have had to
introduce the top type explicitly again.
On the other hand if we declare a protocol Any and define protocol A {...} to
mean protocol A: Any {...} there is not really something special in the
compiler except for adding the conformance which seems very minor to me.
Everything else is just standard behavior of the type system.
> Read Chris' original announcement.. He describes P&Q as it would be adopted
> today as being just a CORNER CASE of a single general principal... a single
> grammar that can work today to describe P&Q as well as generalize
> existentials tomorrow. No special treatment, single parser, single rule. I
> don't like to write un-necessary IF statements in code.
Sorry, I do not understand what you mean here: where would you have to write
unnecessary if-statements?
>
>>>> Why should the top type have special *syntax*? It is just the type all
>>>> other types conform to. No need to do something special here and therefore
>>>> no need to invent an alternative syntax like `Any<>` or the alternative
>>>> from your gist which is rather confusing IMO (and I don’t like the special
>>>> case given to classes in the syntax).
>>> The _[] case is just a degenerate case of the syntax, showing that it is
>>> expressible inside, as opposoed to have to define a contextual keyword
>>> (read the SourceKit code). And then it is aliasable. Part of the problems
>>> in swift today to me is that some things are no doable in swift, so the
>>> compiler must contain that semantic. This here is just one example, but
>>> there are others. These are notions that the standard library has to defer
>>> to the compiler. Some of them have been tabled for 4.0 it seems. My point
>>> here was that it is not fate, and choosing the syntax carefully for
>>> existentials (whichever it is, i don't really care inthe end) would prevent
>>> having to add a magic keyword for to top type to the compiler and to
>>> SourceKit again (they are trying to remove them).
>>
>> `Any` would *not* be a keyword. It is just a type name like `Collection` or
>> `Int`. Like I said, the only magic would be in adding `: Any` to type
>> definitions without a conforming clause.
>
> I hope that by now you understand what magic I was talking about.
>
>>
>>>
>>> As for the current Any<...> proposal for generalizing existentials it is
>>> IMHO cluncky and magic. There is nothing stopping us mechanically from
>>> entering Any<UITableView, UIButton>. To me that is the holemark of bad
>>> design. In what I tested you just can't do it and the reason is clear. Of
>>> course when I
>>
>> `Any<UITableView, UIButton>` is just an intersection type and would be
>> written UITableView & UIButton. And, yes, that would be ok, because it would
>> be just the empty set, i.e. the bottom type (which has no members). There is
>> no magic involved, it is just the normal result of an intersection: each
>> type is a set containing all instances of this type (instances conforming to
>> it)
>
> You can't be serious? You are saying that to you the ide should not be
> telling us we are writting an absurdity? And this one was obvious, but it
> gets a lot worse with more complex types.
Why is an empty intersection absurd? The beauty is that all type expressions
sort out automatically by applying simple set rules. And it actually does make
sense!
struct Set<T> {
// answer any one element
func any() -> T?
}
func intersect<T, U>(a: Set<T>, b: Set<U>) -> Set<T & U> {...}
let x: Set<UITableView> = ...
let y: Set<UIButton> = ..
let z = intersect(x, y) // has type Set<Bottom>
z.any // has type Optional<Bottom> and therefore can only be nil
Therefore the type system statically knows that the intersection of those sets
is always empty. No need to declare this as invalid. It just works correctly
and gives the results you would expect without need for special casing and
compiler magic (which we both would like to keep small).
-Thorsten
>> . Intersecting two sets might result in an empty set. The type denoting the
>> empty set is the bottom type which is the subtype of all types and might be
>> called `Nothing` or `Never` or `Bottom`.
>> Ceylon makes very nice use of type intersections and type unions and the
>> beautiful thing is that these type operations really just work like you
>> would expect if you think of types as sets (which is the standard definition
>> for a type AFAIK). No surprises and no magic there!
>>
>> So it is *not* a sign of bad design, quite to the contrary! What did you
>> test it with? Probably not Ceylon, because otherwise you would have seen
>> that it just works.
>
> Hey, who knows, ceylon may one day come to llvm...
>
>>
>>
>>> say you can't I do not mean that your keyboard will zap u if you try. But
>>> the way to verify correctness is different... and in a world where xcode
>>> would be a good ide, then code completion would even show you why and
>>> actually truly assist (because the grammar i tested makes really makes it
>>> possible). I know that xcode is only as good as SourceKit lets it be.
>>>
>>>>>
>>>>>> Essentially `Any<Collection>` in Swift is just the same as
>>>>>> `Collection<?>` in Java (assuming for comparability’s sake that Swift’s
>>>>>> Collection had no additional associated types; otherwise I would just
>>>>>> have to introduce a Collection<Element, Index> in Java).
>>>>>>
>>>>>> Likewise `Any<Collection where .Element: Number>` is just the same as
>>>>>> `Collection<? extends Number>` in Java.
>>>>> Java supports co/contra variant params
>>>>
>>>> Java has no declaration-site variance like Ceylon or Scala have (see e.g.
>>>> http://ceylon-lang.org/blog/2014/07/14/wildcards#why_i_distrust_wildcards_and_why_we_need_them_anyway).
>>>>
>>>> Java’s wildcards are a way to express use-site variance. The proposed
>>>> `Any<>` does just the same.
>>>>
>>>>
>>>>>
>>>>>> And just like Collection<?> does not conform to a type parameter `T
>>>>>> extends Collection<?>` because Collection<?> is the type `forall E.
>>>>>> Collection<E>` whereas `T extends Collection<?>` is the type `T.
>>>>>> Collection<T>` for a given T.
>>>>>
>>>>> This picture is accurate today, but there are going to be more serious
>>>>> differences after 10 no date is currently geven for when it will come)
>>>>
>>>> You mean Java 10?
>>>
>>> Yes. After 10. Than is their only date hint.
>>>
>>>>
>>>>
>>>>>
>>>>>> In essence protocols with associated types are like generics with
>>>>>> wildcards.
>>>>>
>>>>> Yes, java has kept everything within its generics system rather than
>>>>> split parts out. Something people may not immediately think about with
>>>>> respect to the 2 generic systems is that when u call a func<T>capture(T
>>>>> t){} in java with a wildcard you are doing a compile time capture only
>>>>> (to avoid the dreaded unsafe casts), whereas it is really nice to do the
>>>>> same in swift and subsequently be able to access T.Type and see that it
>>>>> is not Any. The closest u ever get to that type at runtime in java is via
>>>>> generics introspection, but u still can't do everything ( like no new T()
>>>>> ). But today the bridging between existential types and generics is
>>>>> definitely a work in progress.
>>>>>
>>>>>> Coming back to the questions whether (a) allowing existentials to be
>>>>>> used as types is useful and (b) whether sacrificing type safety would
>>>>>> somehow be necessary for that, I think we can safely answer
>>>>>> (a) yes, it *is* useful to be able to use existentials like
>>>>>> Any<Collection> as types, because wildcards are quite often needed and
>>>>>> very useful in Java (they haven’t been added without a reason)
>>>>>
>>>>> IMO they made java 8 (referring to streams). And even though the syntax
>>>>> for co/contra variance is pretty heavy, it is the foundation for all
>>>>> modern java code. The any-fication of the generics is going to open new
>>>>> doors as some of it will translate into a partial reification in the jvm.
>>>>> It seems the decision for now is to not use the extra info in java to
>>>>> retain binary compatibility with all the erased code out there, this is
>>>>> something scala might use in areas where it won't mind loosing java
>>>>> compatibility.
>>>>>
>>>>>> (b) no, sacrificing type safety does not make sense, as the experience
>>>>>> with Java’s wildcards shows that this is not needed. Especially if
>>>>>> something like path dependent types is used like proposed and some
>>>>>> notation to open an existential’s type is added, which is both something
>>>>>> that Java does not have.
>>>>>
>>>>> I hope typesafe opening inside the " if let " syntax gets added. I know
>>>>> that chris is against sugaring, but I played if an implementation of
>>>>>
>>>>> ... x is String?
>>>>> If let! x {}
>>>>> That runs as
>>>>> if let x = x {}
>>>>>
>>>>> something equally short could be done here.
>>>>>
>>>>>>
>>>>>> (2) misconception: POP is different from OOP
>>>>>>
>>>>>> It is not. Protocols are just interfaces using subtyping like OOP has
>>>>>> always done. They just use associated types instead of explicit type
>>>>>> parameters for generics (see above). The more important distinction of
>>>>>> Swift is emphasizing value types and making mutation safely available by
>>>>>> enforcing copy semantics for value types.
>>>>>
>>>>> Values are coming to the jvm, which will narrow this gap (like their view
>>>>> identity for value vs ref and the whole deep ==) . I also really like the
>>>>> cow approach of the swift runtime.
>>>>>
>>>>>> But protocols are not really different from interfaces in Java.
>>>>>
>>>>> There is one big difference: default methods, but it seems swift will add
>>>>> that soon.
>>>>
>>>> Swift already has default extension methods, doesn’t it?
>>>
>>> Yes, and no. It has differently dispatched code that can be found to fill
>>> in the gap of the conformance req, yes. But Joe Grof (?) said that there
>>> are no reasons why these could not be added. Having true defaults could be
>>> one way to deal with optional comformance…
>>
>> The dispatch issue only arises for extensions introducing a method that is
>> not declared in a protocol. That is something you *cannot* do in Java.
>> Java’s default methods are implementations for methods declared in
>> interfaces. Swift’s extension methods providing defaults for methods
>> declared in a protocol are dynamically dispatched and should work like
>> Java’s default methods.
>
> I think we should agree to disagree.
>
>
>> (One caveat exists with subclasses where the superclasses didn’t implement
>> the method because I then am not allowed to `override` the default method
>> but that is a bug IMO).
>>
>> -Thorsten
>>
>>
>>
>>>
>>> protocol MyProto {
>>> func mustImplement()
>>> default canImplement() { }
>>> }
>>>
>>> Related data there:
>>> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160516/018560.html
>>>
>>>>
>>>>
>>>>> I also really like how extensions and conformance mix together in swift
>>>>> to bake retro-modelling in and the adapter pattern (spent enough years
>>>>> deep diving inside eclipse to appreciate it).
>>>>>
>>>>>> I would have preferred a unified model using just classes with real
>>>>>> multiple inheritance like Eiffel has and value types just being a part
>>>>>> of that similar to Eiffel’s `expanded` classes. But that ship has
>>>>>> probably sailed a long time ago :-/
>>>>
>>>> I like extensions very much (having used Smalltalk for a long time). I
>>>> like enums for the pattern matching and structs as value types. But having
>>>> to split protocols off instead of using abstract classes makes things more
>>>> complicated IMO.
>>>>
>>>>> -1 i am old school c/c++... i really like protocol, struct, class,
>>>>> extensions, enums. It is a really nice mix that gives objc people room to
>>>>> grow, but I do miss how they are an integral part of generics (i
>>>>> protocols as a replacement and look forward to when they interact better)
>>>>> and namespaces+scoped-imports (c#)... Looking forward to where things go
>>>>> next
>>>>
>>>> Yeah, namespacing/submodules/conflict resolution (when doing imports but
>>>> also when conforming to multiple protocols which has just the same
>>>> problems) are still missing. But I’m optimistic :-) Let’s complete
>>>> generics first, then tackle existentials/type intersections.
>>>
>>> I think I care more about existentials, but only because of the kind of
>>> java i wrote for a living. I just looked at a bunch of opensource swift
>>> libs (particularly for server side swift)... some of it is a real
>>> engineering disaster: 20+ folders, each with 2 source files... or 3 folders
>>> "extensions" "utils" "classes". Swift is currently not equiped for people
>>> to write big things with... I wish the team would address it sooner than
>>> later (look at their own c++ code to see the difference). IMHO import
>>> conflicts are more often the symptom of bad code than a real issue.
>>
>> Alas, most languages suffer from poor module systems. A good module system
>> should not only allow resolving conflicts between modules and making it
>> possible to structure code well, but solve the issue around versioned
>> modules so that is is possibly to safely use different versions of the same
>> module in the same application.
>>
>> -Thorsten
>>
>>
>>>
>>> Cheers
>>>>
>>>> -THorsten
>>>>
>>>>
>>>>>
>>>>>> So be it. But at least there should be no reasons for POP vs OOP wars ;-)
>>>>>> (I’d like to add that I liked Dave’s talks at last WWDC very much, it’s
>>>>>> just that I don’t think that POP is something new or different.)
>>>>>
>>>>> I used to thin that way. But today I think that although in broad brush
>>>>> strokes the similarities and bigger than the differences, there is room
>>>>> for making a bigger difference in the how.
>>>>>
>>>>>>
>>>>>>
>>>>>> -Thorsten
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution@swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
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