I find myself agreeing with the idea that ad hoc enums are to enums as
structs are to tuples. Based on that analogy, why should an ad hoc enum
*need* a name (autogenerated or otherwise) any more than a tuple needs a
name? Would those who dislike ad hoc enums argue that this also shouldn't
be allowed:
func foo(bar: (x: Int, y: Int)) {}
let t: (x: Int, y: Int) = (x: 5, y: 5)
If someone writes `(.fit | .fill)` (or whatever the hypothetical syntax
might be), that should just *be* the type the same way that `(x: Int, y:
Int)` is a type without a name, and that type can be used in argument
lists, variables, or whatever. There shouldn't be any worry about
declarations across multiple functions colliding or being incompatible any
more than we would worry about two functions declaring arguments of type
`(x: Int, y: Int)` would collide or be incompatible.
One side of ad hoc enums that I'd like to see explored is that, by being
unnamed, they're basically anonymous finite sets and we could apply
well-defined subset relationships to them: in other words, we could
consider allowing this:
func foo(bar: (.fit | .fill)) {
baz(bar: bar)
}
func baz(bar: (.fit | .fill | .florp) { ... }
In other words, an ad hoc enum T can be used wherever an ad hoc enum U is
expected if T ⊆ U.
On Wed, Jun 1, 2016 at 1:43 PM L. Mihalkovic via swift-evolution
<[email protected] <mailto:[email protected]>> wrote:
> On Jun 1, 2016, at 6:51 PM, Vladimir.S <[email protected]
<mailto:[email protected]>> wrote:
>
> Yes, I also can support the idea of autogenerated type name (like
Enum_fit_OR_fill) as long as it allows to do all the things we are
discussing here: declare (.fit|.fill) in function, use .fit on calling
side, use (.fit|.fill) to declare temporary variable of type compatible
with such function parameter etc.
>
It all works because the compiler is just being a thoughless scribe
that just writes the standard enum we don't bother to write ourselves.
Because the heuristic is simple and straightforward then it is
predictible. The enum can be used with its long name be ause it is a
real enum. And writing the short form of it also works because the
compiler knowns uniquely what the long name is everytime it runs into
the short name.
> But how do you suggest to define a type of such function in
`typealias` for example? i.e. for func my(option: (.fit|.fill) {..}
>
> typealias MyFunc = ((.fit|.fill)) -> ()
> or as
>
> typealias MyFunc = (Enum_fit_OR_fill) -> ()
>
Ideally there is no difference whatsoever, there is a single enum, it
is produced at the module level, and it has the long form name.
There can be rules that would prevent us from doing that with
externally visible APIs, if the core team fuges that we should take the
time to write our enums manually and cleanly to make them visible to
the world, but it is not a necessary rule.
>
> But I still can't support the idea of limiting the usage of such
enums - i.e. "To deal with milti site definition, the compiler would
simply flag a error/warning, or be silent in the presence of a new
annotation:". I really think we need then introduce the same rule for
tuples - so no one can use the same tuple declaration in function -
they then should declare separate struct type or use @something for
such functions. Nobody wants such rule for tuples.
>
Multi site thing is not a limitation... Is is a proposed rule to say
that we are able to be lazy twice without being penalized. Yhe compiler
does not like when we define the same thing twice, and thse short form
amount to doing what he does not let us do. But because this is about
concise and lazy, then the compiler can let us get away with it if we
use an annotation that lets it know that "it is not a mistake.. I
really dont want to write that enum myself, even though I am using the
same abbreviation twice". Otherwise, the compiler would let us know
that the second time could be a mistake because there is already
something with the same name...
But again this is a separate idea from the core notion of a syntax
sugaring for writing real enums the lazy (clever) way
>> On 01.06.2016 19:04, L. Mihalkovic wrote:
>> The only problem with this proposal is to consider them ad-hoc
enums... If we view them as having nothing ad-hoc about them and the
thing to be a simple sugaring exercise, then I think all the opositions
on grounds of breaking the language disapear. It still does not mean it
should be done if the core team does not like the idea of encouraging
laziness, or simply do not like what it makes them look like. No matter
what, this type of sugaring exercise has been clearly stated as out of
scope for 3.0
>>
>>>> On Jun 1, 2016, at 2:38 PM, Vladimir.S via swift-evolution
<[email protected] <mailto:[email protected]>> wrote:
>>>>
>>>> On 01.06.2016 11:00, Austin Zheng wrote:
>>>> Tuples are a structural type, they are described entirely by the fact
>>>> that they are a tuple, plus their contained types.
>>>>
>>>> Enum cases are not individual types; that precedent exists nowhere in
>>>> Swift. You can't (yet) build a structural type out of something that
>>>> isn't a type. The fact that you had to propose something like
>>>> "AdhocEnumFitFill_2383748" as an autogenerated name for the type
>>>> demonstrates the proposal's weaknesses: a tuple is an ad-hoc type that
>>>> describes itself, while an anonymous enum isn't.
>>>
>>> Yes, I understand the point about the type of such adhoc enum.
>>> The only workaround I can see in this case(if we'd really want to
have it in language) if adhoc enum type will be `(.Fit|.Fill)` i.e.
textual representation if the declared type. As I understand this also
could not be a solution.. I.e. for example
`(Int,String,(.Fit|.Fill))->String`
>>>
>>> From other point of view, adding such type to typesystem will add
some consistence : you can create a function that don't need definition
of separate structure type(tuple will be used) and don't need separate
enum type(ad-hoc enum will be used). I.e. all data the function needs
to process could be described in function definition. Today we need to
use ugly Bool flags in case we want to achieve the same target.
>>>
>>>>
>>>> Now if enum cases were equivalent if they had the same name (like how
>>>> "Int" means the same thing no matter what tuple or generic type it is
>>>> used in), we'd have a good foundation for a self-describing structural
>>>> type. But this isn't how the existing named enum types work. Why would
>>>> it be a good idea to make anonymous enum cases interchangeable by
name?
>>>> Properties on different types aren't interchangeable, even if they
have
>>>> the same type. In fact, no type member that I am aware of is
>>>> interchangeable solely on the basis of name. An
"ArtistAction.Draw" and
>>>> "CowboyAction.Draw" might have the same name, but they mean completely
>>>> different things.
>>>
>>> I don't think they should be 'interchangeable by name', but just
like tuples if you defined adhoc enum with exactly the same cases as
ad-hoc enum in function parameters - then they are of the same type.
>>>
>>> I.e. :
>>>
>>> func foo(option: (.fit|.fill)) {..}
>>>
>>> foo(.fit) // .fit is of type (.fit|.fill) from definition
>>>
>>> let e : (.fit|.fill) = .fit
>>> foo(e) // e is of (.fit|.fill) type, equal to definition
>>>
>>> but
>>>
>>> func foo2(option: (.fit|.fill|.other)) {..}
>>>
>>> foo2(.fit) // ok, here .fit is of (.fit|.fill|.other) type
>>> foo2(e) --> Error, e is not of type (.fit|.fill|.other)
>>>
>>>>
>>>> Finally, I have to ask: if you are updating your anonymous enum in
>>>> multiple places, how much effort have you actually saved over a
one-line
>>>> enum definition? In fact, tuples are a great example of this: best
>>>> practices usually state that they are good for ad-hoc destructuring,
>>>> such as retrieving multiple return values from a function or pattern
>>>> matching across several values at once, but structs are better
used for
>>>> almost everything else, since they carry semantic meaning that tuples
>>>> don't.
>>>>
>>>
>>> Just the same pros and cons for ad-hoc enums vs enum declaration as
for tuples vs struct declaration. Yes can use it with care and you can
use it in wrong way.
>>>
>>> Btw, I feel like this could be very handy to return adhoc enum:
>>>
>>> func something() -> (.one|.two|.three) {...}
>>>
>>>> I hope that clarifies my thoughts on the matter.
>>>>
>>>> Best, Austin
>>>>
>>>>
>>>>> On Jun 1, 2016, at 12:36 AM, Vladimir.S <[email protected]
<mailto:[email protected]>> wrote:
>>>>>
>>>>> On 01.06.2016 9:55, Austin Zheng via swift-evolution wrote:
>>>>>> Maybe it's overkill. My personal opinion is that breaking the
>>>>>> symmetry of the language like this (are there any other types of
>>>>>> function arguments that cannot be passed as either variable values
>>>>>> or literals?) is too much a price to pay. Your library thinks it's
>>>>>> being clever and vends its functions as taking anonymous enum flags,
>>>>>> and now there are a bunch of things I can't do with those functions
>>>>>> anymore.
>>>>>>
>>>>>> A regular enum can be declared in one line anyways:
>>>>>>
>>>>>> enum ScaleCropMode { case Fit, Fill }
>>>>>
>>>>> Why do we have tuples? Struct could be defined by one line `struct
>>>>> SomeValue { var x = 0, y = 0 }` ;-) I.e. from my point of view
>>>>> developer should decide what he/she wants to use: ad-hoc enum or
>>>>> defined enum type *exactly* as now he/she can decide to use the same
>>>>> tuples in multiply functions instead of one defined struct type.
>>>>>
>>>>> I replied regarding the variable on other message. (In short: I think
>>>>> of the same principle as for tuples: you can declare variable `let e:
>>>>> (.fill | .fit) = .fill` and use it)
>>>>>
>>>>>>
>>>>>> Austin
>>>>>>
>>>>>>> On May 31, 2016, at 11:44 PM, Charles Constant
>>>>>>> <[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>> wrote:
>>>>>>>
>>>>>>>> It breaks the ability to pass in a variable containing the
>>>>>>>> desired
>>>>>>> value, rather than the literal value itself.
>>>>>>>
>>>>>>> Maybe that's appropriate? If the caller is not passing in a
>>>>>>> hardcoded enum case, then that enum is probably general enough
>>>>>>> that it warrants a normal enum. But there are also situations
>>>>>>> where the same function is called from several files in the same
>>>>>>> code-base with different flags. Those are situations where it
>>>>>>> feels like overkill to clutter up my codebase with separate enums,
>>>>>>> only used by a single function.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Tue, May 31, 2016 at 9:24 PM, Austin Zheng via swift-evolution
>>>>>>> <[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>
>>>>>>> wrote:
>>>>>>>
>>>>>>> I admire the desire of this proposal to increase the readability
>>>>>>> of code. I'm -1 to the proposal itself, though:
>>>>>>>
>>>>>>> - It breaks the ability to pass in a variable containing the
>>>>>>> desired value, rather than the literal value itself. (Unless you
>>>>>>> actually want a not-so-anonymous enum type whose definition
>>>>>>> happens to live in a function signature rather than somewhere
>>>>>>> you'd usually expect a type definition to live.) - It breaks the
>>>>>>> ability to store a reference to the function in a variable of
>>>>>>> function type (ditto). - Almost every time I've wanted to use one
>>>>>>> of these "anonymous enums" in my code, I've ended up needing to
>>>>>>> use that same enum elsewhere. In my experience, 'lightweight
>>>>>>> enums' don't end up saving much time compared to a full-fledged
>>>>>>> one.
>>>>>>>
>>>>>>> Like Brent said, I have to say no to any proposal that tries to
>>>>>>> make enums synonyms for numerical values. What happens if you
>>>>>>> rearrange your anonymous enum cases between library versions? Do
>>>>>>> you somehow store an opaque case-to-UInt8 table somewhere for
>>>>>>> every anonymous enum you define for resilience? What happens when
>>>>>>> people start bringing back terrible C patterns, like doing
>>>>>>> arithmetic or bitwise ops on the underlying case values? At least
>>>>>>> you have to try pretty hard as it is to abuse Swift's enums.
>>>>>>>
>>>>>>> Austin
>>>>>>>
>>>>>>> On Tue, May 31, 2016 at 8:25 PM, Brent Royal-Gordon via
>>>>>>> swift-evolution <[email protected]
<mailto:[email protected]>
>>>>>>> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
>>>>>>>
>>>>>>>> And the obvious answer is you can have up to 255 of these babies
>>>>>>>> for the anonymous enum type, and be able to pass numerical
>>>>>>>> equivalents UInt8 with compile time substitution. That the
>>>>>>>> ad-hoc enumeration is basically a syntactic shorthand for UInt8,
>>>>>>>> with an enforced upper bound compile time check simplifies
>>>>>>>> everything including switch statements.
>>>>>>>
>>>>>>> If I wanted a language like that, I'd be writing C, not Swift.
>>>>>>>
>>>>>>> -- Brent Royal-Gordon Architechies
>>>>>>>
>>>>>>> _______________________________________________ swift-evolution
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<mailto:[email protected]>
>>>>>>> <mailto:[email protected]
<mailto:[email protected]>>
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________ swift-evolution
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>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
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