[swift-evolution] [Review] SE 0192 - Non-Exhaustive Enums

[Jason Merchant]

There are a number of things being talked about in this thread, all of
which are solved by proper automated IDE tooling.

Javier, In my opinion the situation you've described is based on how
overall nil is handled by the language parser before it generates LLVM IR.

A smart compiler would know what to do here without any changes to the
language syntax. (Having implemented a similar language parser for LLVM IR,
I can say for certain there is no excuse for the ugly syntax choices that
Swift has been making, and it appears to me the result of laziness and bad
design choices)

I solved this without setting a value before the switch/case statements and
without forcing a default clause to be written. No doubt, it has been clear
that these things appear troubling because of the incorrect design choices
and approach to the underlying problem.

I will present another situation outside of the realm of enums in which
Swift syntax has been made incorrect syntax choices in the handling of nil.

The most obvious is optionals. There are several things wrong with the
swift implementation of optionals:

A: When an object is nil, swift syntax itself changes to try to protect the
user. This results in extra code the developer has to type, even if they
program in genres in which optional situations are irrelevant. (Forcing the
user to unwrap optionals with things like "if let" and "guard" is ugly,
bloated, and unnecessary) In my implementation I have seen that there is no
need for optionals to be written like this in the syntax.

B: The symbols "?" and "!" are littered throughout code needlessly as *compiler
hints*. Meaning the swift parser programmer team was essentially too lazy
to implement what I'm describing and sacrificed the syntax of the language
to avoid writing a parser that would be able to know if something was set
or nil without adding extra garbage to the syntax. Again in my
implementation, I have verified that this can be done and in fact if done
correctly, the resulting* compile time is faster* than the swift compiler,
and the code is cleaner.

What is happening in this thread is that there are core underlying
philosophies that the swift design has adopted which are incorrect
approaches to big picture problems. As a result of swift making these big
picture mistakes, there arise a plethora of these other troubles that come
as domino effects in circumstances here and there. This is why there is a
lot of talk about patching the syntax here or there, and forcing things to
be written, and then down wind of this trail of derailed logic, there arise
a number of people debating what grammar to use for something that
shouldn't be written in the first place. If the big picture problem is
solved, the majority of these discussions are mute.

If Swift can accept that these choices were incorrect, we can cleanup the
syntax and rewrite the parser within an impressively short time as I've
seen myself. However, this requires the agreement of those involved, and
based on this thread and the fact that this line of derailed logic has gone
on for several years, means that the likely response to what I'm suggesting
is one of "That sounds like a lot of work to change, and I already spent a
lot of time and effort making it like this" - Laziness is no excuse for
sticking to bad choices made in the past and causing more bad syntax
choices to be made in the present. If we are truly going to make swift the
dominant language for the future, then we have to adopt a different
attitude toward rewriting design flaws as a community.

We can't always see into the future and know if a choice will be good or
bad, but when we are far enough along the trail to see that the choices
swift made in the past and are a core part of the language, are in fact the
root of the problem, rather than clinging to backward compatibility of a
clearly misguided architecture, *we should do the wise thing and rewrite
the foundation of the language to be built on solid concepts of what we
have learned from the mistakes.*


_______________

Sincerely,
Jason




On Sat, Jan 6, 2018 at 8:07 PM, Javier Soto <javier.api at gmail.com> wrote:

> Why isn't that a problem today? Like I showed in that example, that's
> undefined behavior and will potentially result in a bug (or even a crash if
> instead of an int you end up with an unexpected nil pointer)
>
> On Sat, Jan 6, 2018 at 4:47 PM Jon Shier <jon at jonshier.com> wrote:
>
>> Which isn’t a problem right now, AFAICT. Apps compiled under older SDKs
>> continue to work fine (sometimes better than when compiled under the new
>> SDK, as the older one avoids new bugs). My question is about how that
>> compatibility is accomplished today and how and why the Obj-C and Swift
>> cases are apparently different here.
>>
>>
>>
>> Jon
>>
>> On Jan 6, 2018, at 6:12 PM, Javier Soto <javier.api at gmail.com> wrote:
>>
>> What doesn't happen today? The issue is not when they ship a new SDK:
>> When rebuilding your app against it, you'll get a warning for a missing
>> case. The problem is when running the app against a newer iOS version with
>> a newer version of the SDK where the enum has a new case.
>> On Sat, Jan 6, 2018 at 3:10 PM Jon Shier <jon at jonshier.com> wrote:
>>
>>> Except it clearly doesn’t happen today when Apple ships new SDKs.
>>> Obviously there’s an alternate mechanism used in that case. I’m just
>>> curious what it is and why Swift so desperately needs an alternative.
>>>
>>>
>>> Jon
>>>
>>> On Jan 6, 2018, at 5:49 PM, Javier Soto <javier.api at gmail.com> wrote:
>>>
>>> This is very much an issue in Obj-C today. If you have an NS_ENUM
>>> defined with cases A, B, and C, this switch is correct:
>>>
>>> int foo;
>>> swith (e) {
>>> case A: foo = 0; break;
>>> case B: foo = 1; break;
>>> case C: foo = 2; break;
>>> }
>>>
>>> (Note the lack of a default case)
>>>
>>> If that enum is defined in a framework and it changes after the app is
>>> compiled (like it's the case with Apple frameworks), then that code
>>> produces no warning, yet the foo variable will have a garbage value
>>> (undefined behavior, but as far as the compiler can tell at compile time
>>> your code is fine)
>>>
>>> Adding a default clause to that switch has the downside of not getting
>>> warnings for new added cases, like has been discussed before, which is very
>>> useful.
>>> On Fri, Jan 5, 2018 at 7:11 PM Jon Shier via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>>
>>>> At this point I think it might be useful to outline how binary
>>>> compatibility works for Objective-C on Apple platforms right now. As an app
>>>> developer I’m not intimately familiar with what happens when you run an app
>>>> compiled with the iOS 10 SDK on iOS 11. Are there just runtime checks to
>>>> call old code paths or something else? The more this thread goes on the
>>>> more confused I get about why Swift would have this issue while it doesn’t
>>>> appear to be one for Obj-C. If an enum adds a case now, I don’t have to
>>>> care until I recompile using the new SDK. Is the intention for Swift to be
>>>> different in this regard?
>>>>
>>>>
>>>>
>>>> Jon Shier
>>>>
>>>> On Jan 5, 2018, at 6:41 PM, Jordan Rose via swift-evolution <
>>>> swift-evolution at swift.org> wrote:
>>>>
>>>>
>>>>
>>>> On Jan 3, 2018, at 00:54, Jason Merchant via swift-evolution <
>>>> swift-evolution at swift.org> wrote:
>>>>
>>>> Is it hard to imagine that most everyone can get what they want and
>>>> keep the syntax clean and streamlined at the same time? Without any "@"
>>>> signs or other compiler hints?
>>>>
>>>>
>>>> For what it's worth, the original version of the proposal started with
>>>> a modifier (a context-sensitive keyword, like 'final'), but the core team
>>>> felt that there were a lot of modifiers in the language already, and this
>>>> didn't meet the bar.
>>>>
>>>>
>>>> "Rather, we are how to enable the vendor of a nonexhaustive enum to add
>>>>> new cases without breaking binaries compiled against previous versions"
>>>>
>>>>
>>>> When an enum changes, and the change causes the code to break, the user
>>>> can be presented with migration options from an automated IDE tool. In what
>>>> specific way does this not solve the issue about having to upgrade your
>>>> code when using someone else's code library? This very notion implies your
>>>> disgruntled about doing work when things are upgraded, is that really what
>>>> this fuss is all about?
>>>>
>>>> A well written language interpreter and auto-tooling IDE would not need
>>>> hints embedded in the code syntax itself. Migration hints from version to
>>>> version should not be a part of either the past or future version of the
>>>> code library.
>>>>
>>>>
>>>> Thanks for bringing this up! Unfortunately, it falls down in practice,
>>>> because if there's a new enum case, *it's unclear what you want to do
>>>> with it.* If you're handling errors, it's not obvious that the way
>>>> you've handled any of the *other* errors is appropriate. In the
>>>> (admittedly controversial) SKPaymentTransactionState case, none of the
>>>> existing code would be appropriate to handle the newly-introduced
>>>> "deferred" case, and nor could StoreKit provide "template" code that would
>>>> be appropriate to the client app.
>>>>
>>>>
>>>> In any case, though, the key point on this particular quoted sentence
>>>> is "without breaking *binaries"*. Any such change must be valid
>>>> *without* recompilation, and indeed without any intervention from the
>>>> developer or an IDE, because that's what happens when the user updates
>>>> their OS.
>>>>
>>>> Jordan
>>>>
>>>>
>>>>
>>>>
>>>> ...
>>>>
>>>> I don't expect the community to agree on language grammar, but the
>>>> common sense here on how to achieve the intended goals seems to be out of
>>>> wack.
>>>>
>>>> If someone can present a clear logical statement as to how an automated
>>>> migration tool behind the scenes in the IDE to handle all your versioning
>>>> worries, does not make this whole discussion about adding more convoluted
>>>> syntax additions irrelevant, I'd love to hear it.
>>>>
>>>> ___________________
>>>>
>>>> Sincerely,
>>>> Jason
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Tue, Jan 2, 2018 at 12:36 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>>>
>>>>> On Tue, Jan 2, 2018 at 12:11 PM, Jason Merchant via swift-evolution <
>>>>> swift-evolution at swift.org> wrote:
>>>>>
>>>>>> I think this whole thing has been unnecessarily convoluted. As a
>>>>>> result, the majority of the replies are rabbit holes.
>>>>>>
>>>>>> In my opinion, the true root of the concept in question is as follows:
>>>>>>
>>>>>> *A list of something is desired:*
>>>>>> 1 - Pancake
>>>>>> 2 - Waffle
>>>>>> 3 - Juice
>>>>>>
>>>>>> *Developer wishes to be able to:*
>>>>>> *A)* Add new things to the list of choices in the future as they
>>>>>> come up with new ideas
>>>>>> *B)* Sometimes select one of the choices to be chosen as the normal
>>>>>> choice if no choice is made by the user
>>>>>>
>>>>>> A and B are *separate desires*. In some circumstances a developer
>>>>>> may want to add a new choice and make it the normal choice when there was
>>>>>> no normal choice was clarified before.
>>>>>>
>>>>>
>>>>> I don't think this is an accurate summary of the problem being tackled
>>>>> here. Rather, we are how to enable the vendor of a nonexhaustive enum to
>>>>> add new cases without breaking binaries compiled against previous versions.
>>>>> There is little here to do with what a "default" should be. Indeed, it is
>>>>> an explicit design decision of Swift not to support types having an
>>>>> implicit default value.
>>>>>
>>>>>
>>>>>> ____________________
>>>>>>
>>>>>> *Part 2:*
>>>>>>
>>>>>> After this simple desire is clear, there should be two discussions:
>>>>>> *A)* In a text only coding language, what would we like the syntax
>>>>>> to look like? (Without regard to past-bias. What should it really be,
>>>>>> forget what mistaken design choices were made in Swift in the past)
>>>>>> *B)* How do we approach making this happen behind the scenes?
>>>>>>
>>>>>> *Bonus:* Given that some of us have changed our approach to
>>>>>> programming significantly beyond text based coding, and into more dynamic
>>>>>> mediums of programming in other niches, and even here and there in Xcode -
>>>>>> I would recommend considering how the IDE would show a modern version of
>>>>>> this concept. I feel too often that Swift design syntax has a *lack
>>>>>> of awareness between the distinctions of what the IDE should do, as opposed
>>>>>> to what the syntax of the language should be*, and what should be
>>>>>> handled behind the scenes by automated tooling.
>>>>>>
>>>>>> _____________________
>>>>>>
>>>>>> *My opinion*, in answering the above questions is in preference to a
>>>>>> simple easy to read and write syntax, something like the following:
>>>>>>
>>>>>> choices Breakfast {
>>>>>>     Pancake, *Waffle*, Juice
>>>>>> }
>>>>>>
>>>>>> If a "default" choice is desired, it is obvious to me that I would
>>>>>> select the choice from the IDE, and it would be visually indicated that it
>>>>>> was the default.
>>>>>>
>>>>>> When changes occur, whether new choices are added, old ones are
>>>>>> removed or changed, or a default is added, changed, or removed - a behind
>>>>>> the scenes automated tool analyzes the changes and presents migration
>>>>>> options through the IDE.
>>>>>>
>>>>>> _____________________
>>>>>>
>>>>>> Sincerely,
>>>>>> Jason
>>>>>>
>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>
>>>>>>
>>>>>
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>>>>
>>>>
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>>>>
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>>>>
>>> --
>>> Javier Soto
>>>
>>> --
>> Javier Soto
>>
>> --
> Javier Soto
>
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