[swift-evolution] [draft] Compound Names For Enum Cases
Daniel Duan
daniel at duan.org
Tue Jan 24 17:44:12 CST 2017
Just to be clear (so may previous point may make more sense), the “name” in the function `func f(x: Int, y: Int) {}` is `f(x:y:)`. The name of `f(a: Int, b: Int) {}` does *not* share a name with the previous function. That’s what I refer to when I talk about names. I would not consider these two being both declared as “overloading”. Here’s a function that I would say is overloading `f(x:y:)`: `func f(x: String, y: String)`.
One of the benefits (as stated in the motivation section of the proposal) is to make enum case’s name consistent with functions in Swift.
> On Jan 24, 2017, at 3:16 PM, Christopher Kornher <ckornher at me.com> wrote:
>
>>
>> On Jan 24, 2017, at 4:02 PM, Daniel Duan <daniel at duan.org <mailto:daniel at duan.org>> wrote:
>>
>>
>>
>> Daniel Duan
>> Sent from my iPhone
>>
>> On Jan 24, 2017, at 2:53 PM, Daniel Duan via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>
>>>
>>>
>>> Daniel Duan
>>> Sent from my iPhone
>>>
>>> On Jan 24, 2017, at 2:18 PM, Christopher Kornher via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>
>>>> I agree that this rule would be consistent with the handing of Swift function signatures, but my proposal is self-consistent and:
>>>>
>>>> 1) It is more powerful, matching on the case name or not as required.
>>>> 2) Is consistent with existing switches that ignore associated values
>>>> 3) Is constant with ignored labels in other Swift constructs (proposed and in past versions of Swift, at least)
>>>> 4) Avoids a possible API change for current enums. This is currently legal but would not be if the enum case “name” is the entire signature for constructing it:
>>>>
>>>> ```
>>>> enum E {
>>>> case a( a: Int )
>>>> case b( a: Int )
>>>> }
>>>>
>>>> let anEmum = E.a( a: 4 )
>>>>
>>>>
>>>> switch anEmum {
>>>> case .a( let x ) :
>>>> break
>>>> case .b( let x ) :
>>>> break
>>>> }
>>>>
>>>> switch anEmum {
>>>> case .a( let y ) :
>>>> break
>>>>
>>>> case .b( let y ) :
>>>> break
>>>> }
>>>> ```
>>>> So is this proposal worth creating a breaking change? I don’t think so. it would be possible to ignore the associated parameter name, but not the type, but that would further confuse case matching, I believe.
>>>>
>>>> I personally don’t see much purpose in having two enum cases with the same name if they are always treated as distinct and there is no way to reason on the case name.
>>>
>>> Would you say the same for functions? Our opinions differ in what constitute a "name". In Swift, function names include parameters. Each enum case declares a function that creates a enum value. That's why it's *more* consistent for enum to have a similar definition of "name".
>>>
>>> As for pattern matching, number of patterns the number of cases being matched have a many-to-one relationships. This is true in Swift and many
>>>
>>
>> (Ah, accidentally sent it on my iPhone. My apologies.)
>>
>> … other languages. What you are proposing complicates the rules by making this untrue. We'd have to special-case this feature in our pattern matching algorithm.
>
> I am not proposing a breaking change. I believe that it is the best way to handle “overloading” enum names without breaking existing code. I don’t believe that this proposal changes any existing logic or rules.
>
> The use of the terms "name” and "signature" is well established in many languages. e.g.: https://en.wikipedia.org/wiki/Type_signature <https://en.wikipedia.org/wiki/Type_signature> I am trying to use the terms in this context.
>
> Sharing a function name (with different signatures) is an aid to understanding the purpose of functions and is part of many languages. I do not believe that extending the concept to enums is worth the cost, especially since it will break existing Swift code.
>
> You are proposing a source breaking change and I do not agree that is is an improvement. What is the benefit of this change?
>
>
>>
>>>> If they are always distinct, then requiring different names eliminates unnecessary cognitive load. There is a good reason for functions to have the same “name” and different signatures, and there are precedents in many languages.
>>>>
>>>> You may disagree, but I believe that enums exist to support reasoning on distinct cases and that muddying that by treating the associated value as part of the “signature" increases the language “surface area” while adding no tangible benefit.
>>>>
>>>>
>>>>> On Jan 24, 2017, at 2:23 PM, Matthew Johnson via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>
>>>>>>
>>>>>> On Jan 24, 2017, at 3:10 PM, Christopher Kornher via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>>
>>>>>> Your example is only has only one case, which is not typical. Perhaps I am missing something, but the only reason that I can imagine for having a case with multiple ways to “construct” it is to have all variants of the case to match. If you don’t want them to match, use a different case name.
>>>>>
>>>>> It sounds like you are missing something. The `bar(a:)` and `bar(b:)` are the full case names. These are *not* the same case. The `bar` shorthand is allowed when there is no ambiguity, however for an enum with both `bar(a:)` and `bar(b:)` there *is* ambiguity and therefore the `bar` shorthand is not allowed. The programmer is required to spell out the full name of the case they wish to match.
>>>>>
>>>>>
>>>>>>
>>>>>> It would still be possible to match on the different types of bar when needed:
>>>>>>
>>>>>> ```
>>>>>> enum Foo {
>>>>>> case bar(a: Int)
>>>>>> case bar(b: String)
>>>>>> case notAbar
>>>>>> }
>>>>>>
>>>>>>
>>>>>> switch aFoo {
>>>>>> case .bar( let a: Int) : // matches Ints only
>>>>>> ...
>>>>>>
>>>>>> case .bar( let b: String) : // matches Strings only
>>>>>> ...
>>>>>> }
>>>>>>
>>>>>> switch aFoo {
>>>>>> case .bar : // Matches both cases and that is a good thing
>>>>>> …
>>>>>>
>>>>>> case notAbar:
>>>>>> ….
>>>>>> }
>>>>>>
>>>>>> ```
>>>>>>
>>>>>>> On Jan 24, 2017, at 5:27 AM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>>>
>>>>>>> I would imagine it would be logical to have it work just like it does now with functions. If case bar is distinct, then that should still work, but if bar is "overloaded," then case bar should be invalid for ambiguity. Seems fine to me, shouldn't break any existing code and therefore we don't lose anything.
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Jan 24, 2017 at 01:13 David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 24 Jan 2017, at 00:52, Joe Groff via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>>>
>>>>>>>> We're not terribly principled about this right now with non-pattern declaration references. You can still reference an unapplied function by its base name alone without its labels, if it's unambiguous:
>>>>>>>>
>>>>>>>> func foo(x: Int, y: Int) {}
>>>>>>>>
>>>>>>>> let foo_x_y: (Int, Int) -> () = foo
>>>>>>>>
>>>>>>>> so it'd be consistent to continue to allow the same in pattern references.
>>>>>>>
>>>>>>> WRT ambiguity, do we loose the ability to pattern match on the naked case name when two cases share the same base name?
>>>>>>>
>>>>>>> enum Foo {
>>>>>>> case bar(a: Int)
>>>>>>> case bar(b: String)
>>>>>>> }
>>>>>>>
>>>>>>> switch aFoo {
>>>>>>> case .bar: // matches both cases
>>>>>>> break
>>>>>>> }
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>>>>>>
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>>>>>
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