I have an enum in C and the index needs to be represented by a String.
How can a Swift enum of String type be used by integer index?
I would like to copy the enum to Swift, set the type to string and define all of the raw values to display text, and then use the C enum value to extract the raw value text for the Swift String enum.
Otherwise I will just create an array of strings.. But the enum would be more usable.
Swift 4.2 introduced CaseIterable which does exactly the same thing without the need to declare an allValues array. It works like this:
enum MyEnum: String, CaseIterable {
case foo = "fooString"
case bar = "barString"
case baz = "bazString"
}
and you can access its values by
MyEnum.allCases
or a value at a specific index by
MyEnum.allCases[index]
In Swift, enum types do not hold its index info of cases (at least, not provided for programmers).
So:
How can a Swift enum of String type be used by integer index?
The answer is "You cannot".
You can bind Int (or enum cases) and String values in many ways other than just create an array of strings..
For example, if your bound Strings can be the same as case labels, you can write something like this:
enum MyEnum: Int {
case foo
case bar
case baz
var string: String {
return String(self)
}
}
if let value = MyEnum(rawValue: 0) {
print(value.string) //->foo
}
If your Strings need to be a little more complex to display text, you can use Swift Dictionary to bind enum cases and Strings.
enum AnotherEnum: Int {
case foo
case bar
case baz
static let mapper: [AnotherEnum: String] = [
.foo: "FooString",
.bar: "BarString",
.baz: "BazString"
]
var string: String {
return AnotherEnum.mapper[self]!
}
}
if let value = AnotherEnum(rawValue: 1) {
print(value.string) //->BarString
}
A little bit more readable than a simple array of strings.
Simple workaround which is also useful if you want to enumerate a string enum.
enum MyEnum: String {
case foo = "fooString"
case bar = "barString"
case baz = "bazString"
static let allValues = [foo, bar, baz] //must maintain second copy of values
}
//enumeration advantage
for value in MyEnum.allValues {
print(value)
}
//get value by index
let value = MyEnum.allValues[1]
print(value) //barString
You can add an index as a part of the enum.
enum StringEnum: String, CaseIterable {
case pawn, rook, knight, bishop, king, queen
var name: String { self.rawValue.uppercased() }
var index: Int { StringEnum.allCases.firstIndex(of: self) ?? 0 }
}
And find enum cases by index with the function:
func findEnum(by index: Int) -> StringEnum? {
StringEnum.allCases.first(where: { $0.index == index })
}
allCases.firstIndex(of:) might have O(n) performance, leading to n^2 performance if you use it in a loop.