Perhaps if enums were automatically indexed by the compiler for the order of
the case declerations?
enum Food {
case Fruit
case Vegetable
case Meat
}
Food.Fruit.index == 0
Food.Vegetable.index == 1
Food.Meat.index == 2
3. Re: Proposal: Enum 'count' functionality (Joe Groff)
Message: 3
Date: Tue, 22 Dec 2015 07:24:37 -0800
From: Joe Groff <[email protected]>
To: Zef Houssney <[email protected]>
Cc: Swift Evolution <[email protected]>
Subject: Re: [swift-evolution] Proposal: Enum 'count' functionality
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
On Dec 21, 2015, at 10:33 PM, Zef Houssney <[email protected]> wrote:
I agree with Stephen Celis that the best names for this (yet) are definitely
`cases` and optionally `rawValues` if the cases are RawRepresentable.
Regarding handling cases with associated values where some of those values are
other enums, it seems odd to me to try to return every variation of each case.
I can’t picture how that would work sanely when there are multiple associated
values, such as a case like `MyCase(String, SomeEnum)`. Therefore I prefer the
idea of having the array contain the constructor for cases with associated
values. The main problem I see here is that the type system (as far as I know)
can’t fully represent that type of thing, but I think it’s still potentially
valuable. Related to this I’m putting together a separate proposal that
explores a bit more on why I believe the enum constructor to be valuable,
though that’s in a bit of a different context.
Generating a list of values for MyCase(String, SomeEnum) wouldn't make sense
because there are an infinite number of Strings, so Strings don't make sense as
a value-enumerable type. However, you could have a mostly-flat enum that uses
subenums for organization:
enum Food {
enum Fruit {
case Apple, Banana, BellPepper
}
case fruit(Fruit)
enum Meat {
case Beef, Pork, Venison
}
case meat(Meat)
}
In many C family code bases it's common to group related enums by order, even if there's
otherwise no intrinsic order among the elements. Preserving the structure of the cases in the
type system makes them easier to understand and work with in pattern-matching, since you can
handle all fruits by matching `.fruit(_)` instead of having to maintain `food >=
FirstFruit && foo <= LastFruit` ranges. For these kinds of enums, recursively
generating the associated values is still useful.
-Joe
I shared these thoughts in a bit more detail here a couple weeks ago, with some
followup in the next two messages:
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001864.html
Zef
On Dec 21, 2015, at 3:58 PM, Erica Sadun via swift-evolution
<[email protected]> wrote:
That would be okay too. Thank you, Santa Joe.
-- E, who hopes she was on the nice list.
On Dec 21, 2015, at 3:56 PM, Joe Groff <[email protected]> wrote:
On Dec 21, 2015, at 12:24 PM, Erica Sadun <[email protected]> wrote:
I could be satisfied by such an approach. I could even be more satisfied if
enum Foo: ValueEnumerable { case A, B, C }
were also essentially an alias for
enum Foo: Int, ValueEnumerable { case A=0, B, C }
:)
If the value collection were sufficiently capable, you wouldn't necessarily
need an implicit Int raw value; you could do `allValues.indexOf(.A)` to get the
index for a case.
-Joe
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