Codable synthesis for Swift enums with overloaded associated values

Development Compiler
, ,
1

I was wondering why Codable conformance can't be generated for enums that have overloaded associated values:

enum TestEnum: Codable {
    case value(aDouble: Double)
    case value(anInt: Int)
}
let t1: TestEnum = .value(aDouble: 1.0)
let t2: TestEnum = .value(anInt: 1)

generates an error (swift-DEVELOPMENT-SNAPSHOT-2023-06-26, arm64 macOS):

**testit.swift:2:6:** **error:** **type 'TestEnum' does not conform to protocol 'Decodable'**

Without conforming to Codable the enum seems to work:

enum TestEnum {
    case value(aDouble: Double)
    case value(anInt: Int)
    case value(aBool: Bool)
}

let t1: TestEnum = .value(aDouble: 1.0)
let t2: TestEnum = .value(anInt: 1)
let t3: TestEnum = .value(aBool: true)
print(t1,t2,t3)

prints:
value(aDouble: 1.0) value(anInt: 1) value(aBool: true)

2

Not sure about Codable, but JSONEncoder specifically would encode this into something like:

{ "value":{"aDouble":0}}}

and if there are more than one "value" in the resulting (dictionary) "object" that won't fly. Try making different key for each case, e.g:

enum TestEnum: Codable {
    case doubleValue(aDouble: Double)
    case intValue(anInt: Int)
    case boolValue(aBool: Bool)
}
1 Like
3

Yeah - this works:

enum TestEnum: Codable {
    case doubleValue(Double)
    case intValue(Int)
    case boolValue(Bool)
    static func value(aDouble: Double) -> Self { .doubleValue(aDouble); }
    static func value(anInt: Int) -> Self { .intValue(anInt); }
    static func value(aBool: Bool) -> Self { .boolValue(aBool); }
}
let t1: TestEnum = .value(aDouble: 1.0)
let t2: TestEnum = .value(anInt: 1)
let t3: TestEnum = .value(aBool: true)
print(t1,t2,t3)

I just wish there was a simpler way, without having to do the duplications.

1 Like
4

I know it's a matter of style which to prefer, but maybe just this?

enum TestEnum: Codable {
    case doubleValue(Double)
    case intValue(Int)
    case boolValue(Bool)
}
let t1: TestEnum = .doubleValue(1.0)
let t2: TestEnum = .intValue(1)
let t3: TestEnum = .boolValue(true)

Otherwise, I guess you'd need to implement Encodable/Decodable conformances manually.