[swift-dev] Swift C enum Case Mapping

Ryan Lovelett swift-dev at ryan.lovelett.me
Mon Jan 11 13:22:48 CST 2016


Perhaps I'm not following that parenthetical comment. Are you saying
that even if I could add NS_ENUM to the header it still wouldn't compile
into a true Swift enum (on a non-Apple platform)?

Swift's pattern matching capability is probably a top 3 reason why I am
trying to port my C application to use Swift rather than just straight
C. Not being able to get this nicety out-of-the-box is just part of
doing business on a bleeding edge programming language.

However this *seems* like something that should be able to be achieved.
Looking at the fe_type enum definition, because it had no bit pattern
associated with it, I would have assumed it was a true non-overlapping
enum. Its probable I'm not seeing the whole landscape here so would you
be able to illuminate why isn't this the default?

On Mon, Jan 11, 2016, at 01:11 PM, Jordan Rose wrote:
> Right. This is because Swift can't tell if your enum is actually an
> option set, a true, non-overlapping enum, or just a set of related
> constants, so it picks the lowest common denominator. We currently
> don't have a great way to override that in headers you don't control.
> (Heck, on non-Apple platforms we don't have a great way to do it
> in headers you do control; Swift is currently keying off the
> macro names.)
> Jordan
>> On Jan 10, 2016, at 13:25 , Austin Zheng via swift-dev <swift-
>> dev at swift.org> wrote:
>> I spoke too soon, the cases are also defined as values of that type.
>> So, a working version of your code:
>> extensionfe_type:CustomStringConvertible{
>> publicvardescription:String{ switchself{ caseFE_QPSK:return"QPSK"
>> caseFE_QAM:return"QAM" caseFE_OFDM:return"OFDM"
>> caseFE_ATSC:return"ATSC" default:fatalError("can't be
>> exhaustive")    }  } }
>> Best, Austin
>>> On Jan 10, 2016, at 1:22 PM, Austin Zheng <austinzheng at gmail.com>
>>> wrote:
>>> Hi Ryan,
>>> Apologies, I should have been more clear. In Xcode you can alt(?)-
>>> click on a type (e.g the 'MyType' in "let a : MyType = 123") in the
>>> IDE to pop up a little window that shows you the definition,
>>> including the type and some other information. If you're on a Linux
>>> box or not using an IDE you probably don't have that option.
>>> The only methods I see exposed on the Swift imported type are
>>> initializers taking a integer raw value, and a 'rawValue' property
>>> for getting back out the raw value. Hope that helps.
>>> Austin
>>>> On Jan 10, 2016, at 1:18 PM, Ryan Lovelett <swift-
>>>> dev at ryan.lovelett.me> wrote:
>>>> Austin,
>>>> I guess I should say that the `typedef` is coming from aLinux
>>>> kernel header[1]. So I don't think I'm going to be able to add any
>>>> macros to the definition.
>>>> What do you mean about alt-click? Alt click where?
>>>> On Sun, Jan 10, 2016, at 04:12 PM, Austin Zheng wrote:
>>>>> fe_type is being imported as a struct (alt-click 'fe_type' in
>>>>> Swift). I think if you want it to be imported as an enum you need
>>>>> to use the NS_ENUM macro in the definition, which might not be
>>>>> possible in your case.
>>>>> Austin
>>>>>> On Jan 10, 2016, at 1:06 PM, Ryan Lovelett via swift-dev <swift-
>>>>>> dev at swift.org> wrote:
>>>>>> typedef enum fe_type { FE_QPSK, FE_QAM, FE_OFDM, FE_ATSC }
>>>>>> fe_type_t;
>>  _______________________________________________
>> swift-dev mailing list swift-dev at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-dev


  1. http://lxr.free-electrons.com/source/include/linux/dvb/frontend.h?v=3.2
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