This is really useful and used a lot. And this is safe in meaning compiler
will notify you if you changed the enum - you'll have to change such
constant array.
I wish we'll have something like this in Swift.
Just like .rawValue currently, i.e.
let e = Planet.earth
print(e.mass, e.description)
On Thu, May 26, 2016 at 4:43 PM, Vladimir.S via swift-evolution > <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
Or(if we are sure we'll don't forget to udpate `infoDict` in case of
new added case in future):
enum Planet {
case earth
case moon
struct PlanetInfo {
var mass: Double
var description: String
}
private static let infoDict = [
Planet.earth :
PlanetInfo(mass: 1.0, description:"Earth is our home"),
.moon:
PlanetInfo(mass: 0.2, description:"Just a moon"),
]
var info : PlanetInfo { return Planet.infoDict[self]! }
}
But I agree with you, IMO we need static stored properties for each case.
On 26.05.2016 18 <tel:26.05.2016%2018>:15, Jānis Kiršteins wrote:
The problem is that PlanetInfo values are recreated each time while
they are static. Imagine if PlanetInfo where some type that expensive
to create performance wise.
You could solve it by:
enum Planet {
struct PlanetInfo {
var mass: Double
var description: String
}
case earth
case moon
private static earthInfo = PlanetInfo(mass: 1.0, description:
"Earth is our home")
private static moonInfo = PlanetInfo(mass: 0.2, description:
"Just a moon")
var info : PlanetInfo {
switch self {
case earth: return PlanetInfo.earthInfo
case moon: return PlanetInfo.moonInfo
}
}
}
But that again more verbose. The proposed solution is explicit that
those properties are static for each case.
On Thu, May 26, 2016 at 5:58 PM, Vladimir.S via swift-evolution > <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
I support the proposal, but couldn't the initial target be
achieved today
with such (more verbose,yes) solution? :
enum Planet {
struct PlanetInfo {
var mass: Double
var description: String
}
case earth
case moon
var info : PlanetInfo {
switch self {
case earth: return PlanetInfo(mass: 1.0,
description: "Earth is
our home")
case moon: return PlanetInfo(mass: 0.2,
description: "Just a
moon")
}
}
}
let e = Planet.earth
print(e, e.info.description)
let m = Planet.moon
print(m, m.info.description)
On 26.05.2016 8:26, Charlie Monroe via swift-evolution wrote:
What this proposal is asking for is an easier way to
have derived values
from enum cases. Asking for more flexible RawValues
means mass and radius
are not derived, they are the source of truth. It goes
against the whole
point of RawRepresentable. You are not saying ‘Mercury
is identified by
the case .mercury’, you are saying ‘Mercury is
identified by a mass of
3.303e+23’. It’s backwards.
I see what Janis meant in the first email. It's not that
the planet would
be identified by the mass or radius. It could very much be
case Mercury = 1 where (mass: 3, radius: 2),
- Mercury's rawValue would be 1.
The issue here is that sometimes you want additional
information with the
enum. There are many cases where you extend the enum with a
variable:
enum Error {
case NoError
case FileNotFound
...
var isFatal: Bool {
/// swtich over all values of self goes here.
}
var isNetworkError: Bool {
/// swtich over all values of self goes here.
}
var isIOError: Bool {
/// swtich over all values of self goes here.
}
}
What the propsal suggests is to simplify this to the following:
enum Error {
var isFatal: Bool
case NoError where (isFatal: false, isNetworkError: false,
isIOError:
false)
case FileNotFound where (isFatal: true, isNetworkError:
false, isIOError:
true)
...
}
So that you assign the additional information to the enum
value itself.
Charlie
On 26 May 2016, at 1:47 PM, David Sweeris via
swift-evolution
<swift-evolution@swift.org
<mailto:swift-evolution@swift.org>
<mailto:swift-evolution@swift.org
<mailto:swift-evolution@swift.org>>> wrote:
On May 25, 2016, at 10:27 PM, Jacob > Bandes-Storch <jtbandes@gmail.com > <mailto:jtbandes@gmail.com> > <mailto:jtbandes@gmail.com > <mailto:jtbandes@gmail.com>>> wrote:
On Wed, May 25, 2016 at 8:15 PM, David Sweeris
via swift-evolution
<swift-evolution@swift.org
<mailto:swift-evolution@swift.org>
<mailto:swift-evolution@swift.org
<mailto:swift-evolution@swift.org>>> wrote:
On May 25, 2016, at 7:37 AM, Leonardo
Pessoa via swift-evolution
<swift-evolution@swift.org
<mailto:swift-evolution@swift.org>
<mailto:swift-evolution@swift.org
<mailto:swift-evolution@swift.org>>>
wrote:
Hi,
Couldn't this be solved by using
tuples? If not because the syntax
is not allowed I think this would be
more coherent to do it using
current syntax.
enum Planet : (mass: Float, radius:
Float) {
case mercury = (mass: 3.303e+23,
radius: 2.4397e6)
case venus = (mass: 4.869e+24,
radius: 6.0518e6)
case earth = (mass: 5.976e+24,
radius: 6.37814e6)
case mars = (mass: 6.421e+23,
radius: 3.3972e6)
case jupiter = (mass: 1.9e+27,
radius: 7.1492e7)
case saturn = (mass: 5.688e+26,
radius: 6.0268e7)
case uranus = (mass: 8.686e+25,
radius: 2.5559e7)
case neptune = (mass: 1.024e+26,
radius: 2.4746e7)
}
This would be my preferred solution… AFAIK,
the only reason we
can’t do it now is that Swift currently
requires RawValue be an
integer, floating-point value, or string. I
don’t know why the
language has this restriction, so I can’t
comment on how hard it
would be to change.
- Dave Sweeris
Except you'd have to write
Planet.mercury.rawValue.mass, rather than
Planet.mercury.mass.
This could be one or two proposals: allow enums
with tuple RawValues,
and allow `TupleName.caseName.propertyName` to
access a tuple element
without going through .rawValue.
Good point… Has there been a thread on allowing
raw-valued enums to be
treated as constants of type `RawValue` yet? Either
way, removing the
restriction on what types can be a RawValue is
still my preferred
solution.
- Dave Sweeris
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