Well, I propose the “#” syntax to be consistent with other proposals that
intend to provide compilation-related code. In this case, the proposal is just
a way to provide an indication that a certain field within a struct or class
should be enforced to be a value of a certain enum, not just a plain integer,
by the compiler. Anyhow, I think many different sintaxis could be elaborated.
For example, another possible syntax could imply reusing the typealias
expression:
extension Card{
typealias suit:CardSuit = suit:Int
}
However, I assume that using this syntax it should be possible to directly
assign to the suit field both an integer or a CardSuit.
> El 24 mar 2016, a las 18:43, James Campbell <[email protected]> escribió:
>
> I would rather have a syntax that mirrors the way Protocol does it.
>
> struct Card {
> suit:enum<CardSuit>
> value:Int
> }
>
> or we could change it so this only excepts the enum itself unless you
> explicitly cast from a Int or another enum:
>
> struct Card {
> suit:CardSuit
> value:Int
> }
>
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> On Thu, Mar 24, 2016 at 5:41 PM, Carlos Rodríguez Domínguez
> <[email protected] <mailto:[email protected]>> wrote:
> It is a common practice in C to assign to integer (int, int16, int64, etc.)
> typed variables “constant" values declared in enums. In swift, it is in fact
> possible to do that by using enums' “rawValue” property. When importing
> structs from C into swift, we even get some fields declared with an integer
> type, but expecting the assignment of a “constant” declared inside an enum.
> Of course, this is error prone, it is “old-style” programming and very
> confusing for newcomers. To solve this issue, my proposal is to be able to
> create extensions that promote certain fields within a class or struct to
> enums.
>
> For instance, let’s take these sample C struct and enum:
>
> struct Card {
> int suit;
> int rank;
> };
>
> typedef enum {HEARTS, DIAMONDS, CLUBS, SPADES} CardSuit;
>
> (Note: I understand that above code follows a bad programming practice, yet
> it is widely common)
>
> It should be imported into swift as follows:
>
> struct Card {
> suit:Int
> value:Int
> }
>
> enum CardSuit : Int {
> case Hearts, Diamonds, Clubs, Spades
> }
>
> Now, I propose to be able to create an extension as follows:
>
> extension Card {
> #enumvalue(suit:CardSuit)
> }
>
> From this moment on, the suit field should only receive CardSuit values, thus
> not requiring the use of raw values for assignments.
>
> These extensions should also be of great interest for people using CoreData,
> since it is not possible to declare enums in models. Therefore, to declare
> enums, it is necessary to declare integer values, and then use the “unsafe”,
> “unexpressive" approach explained before.
>
> Note that the proposal intends to only support promotions from integer values
> to enum values, but, for example, it could also be extended to string values.
>
> Finally, it could be appropriate to extend this proposal to redeclare func’s
> signatures, in order to promote certain parameters to enum values.
>
> Best,
>
> Carlos.
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