[SR-30] Enumerations could have a "allValues" property

[swift-ci]

Previous ID	SR-30
Radar	rdar://problem/17102392
Original Reporter	RuiCarneiro (JIRA User)
Type	Improvement
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	6
Component/s
Labels	Improvement, LanguageFeatureRequest
Assignee	@CodaFi
Priority	Medium

md5: 6f9747e0e0648c9bf5fee84b0f66cd7f

relates to:

• SR-3050 enum cases should be enumerable

Issue Description:

Sometimes, it's convenient to have an allValues property for an enum that automatically generates a collection with all possible elements.

eg:

{{enum Fruits { case Apple, Orange, Peach, Banana }

for fruit in Fruits.allValues {
// ...
}}}

{color:red}On another note, it would be handy to have a reverse function for the rawValue propriety

eg:

{{enum Fruits : Int { case Apple = 0, Orange ... }

let fruit : Fruits? = Fruits.reverseRawValue(1)

// fruit == Fruits.Orange}}{color}

Thanks, Kevin Ballard.

[lilyball]

We already have a reverse function for the rawValue property; every RawRepresentable type gets a failable initializer init?(rawValue: Self.RawValue).

As for {{allValues}, I'd like to point out that this could only be done for C-like enums (enums without associated values). It's also not obvious how it should work; does it return an Array or some lazy generator? If it returns an Array, does it generate one on every call, or does it save it as a static value? Generating it on every call has performance implications, but saving it as a static value takes memory. Furthermore, once you have an allValues list, the next natural thing to want is some way to get the previous/next variant from a given variant, but does it actually make sense to do that? Also, making any change like this means automatically adding a member to all C-like enums even when they don't declare any protocol conformance, which may be undesired (maybe I want to have an allValues member that returns something else, e.g. if I have variants in my enum that aren't truly "values" but are instead things like bitmasks if my enum is a set of bitflags).

It seems to me that swift-evolution is the right place to discuss the allValues suggestion.

[moiseev]

CodaFi (JIRA User), found this issue. Hasn't it been fixed recently?

[CodaFi]

Yep. Addressed by the merge of #13655.

[AnthonyLatsis]

Swift evolution proposal: SE-0194.