Convert received Int to Bool decoding JSON using Codable

Property Wrapper

To decode Strings, Ints, Doubles or Bools to a Bool,

just put @SomeKindOfBool before the boolean property like:

@SomeKindOfBool public var someKey: Bool

---

Demo:

struct MyType: Decodable {
    @SomeKindOfBool public var someKey: Bool
}

let jsonData = """
[
 { "someKey": "true" },
 { "someKey": "yes" },
 { "someKey": "1" },

 { "someKey": 1 },

 { "someKey": "false" },
 { "someKey": "no" },
 { "someKey": "0" },

 { "someKey": 0 }
]
""".data(using: .utf8)!

let decodedJSON = try! JSONDecoder().decode([MyType].self, from: jsonData)

for decodedType in decodedJSON {
    print(decodedType.someKey)
}

---

The powerful PropertyWrapper implementation behind this:

@propertyWrapper
struct SomeKindOfBool: Decodable {
    var wrappedValue: Bool

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()

        //Handle String value
        if let stringValue = try? container.decode(String.self) {
            switch stringValue.lowercased() {
            case "false", "no", "0": wrappedValue = false
            case "true", "yes", "1": wrappedValue = true
            default: throw DecodingError.dataCorruptedError(in: container, debugDescription: "Expect true/false, yes/no or 0/1 but`\(stringValue)` instead")
            }
        }

        //Handle Int value
        else if let intValue = try? container.decode(Int.self) {
            switch intValue {
            case 0: wrappedValue = false
            case 1: wrappedValue = true
            default: throw DecodingError.dataCorruptedError(in: container, debugDescription: "Expect `0` or `1` but found `\(intValue)` instead")
            }
        }

        //Handle Int value
        else if let doubleValue = try? container.decode(Double.self) {
            switch doubleValue {
            case 0: wrappedValue = false
            case 1: wrappedValue = true
            default: throw DecodingError.dataCorruptedError(in: container, debugDescription: "Expect `0` or `1` but found `\(doubleValue)` instead")
            }
        }

        else {
            wrappedValue = try container.decode(Bool.self)
        }
    }
}

If you need to implement an optional one, check out this answer here

My suggestion: don't fight the JSON. Get it into a Swift value as quickly and with little fuss as possible, then do your manipulation there.

You can define a private internal structure to hold the decoded data, like this:

struct JSONModelSettings {
    let patientID : String
    let therapistID : String
    var isEnabled : Bool
}

extension JSONModelSettings: Decodable {
    // This struct stays very close to the JSON model, to the point
    // of using snake_case for its properties. Since it's private,
    // outside code cannot access it (and no need to either)
    private struct JSONSettings: Decodable {
        var patient_id: String
        var therapist_id: String
        var enabled: String
    }

    private enum CodingKeys: String, CodingKey {
        case settings
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let settings  = try container.decode(JSONSettings.self, forKey: .settings)
        patientID     = settings.patient_id
        therapistID   = settings.therapist_id
        isEnabled     = settings.enabled == "1"
    }
}

---

Other JSON mapping frameworks, such as ObjectMapper allows you to attach a transform function to the encoding/decoding process. It looks like Codable has no equivalence for now.

In those cases I usually like to keep the model like the JSON data, so in your case Ints. Than I add computed properties to the model to convert into Booleans etc

struct Model {
   let enabled: Int
 
   var isEnabled: Bool {
       return enabled == 1
   }
}

Decode as a String and then convert it to Bool, just modifying some lines of your code:

("0" is a JSON string, and cannot be decoded as an Int.)

struct JSONModelSettings {
    let patientID : String
    let therapistID : String
    var isEnabled : Bool

    enum CodingKeys: String, CodingKey {
        case settings // The top level "settings" key
    }

    // The keys inside of the "settings" object
    enum SettingsKeys: String, CodingKey {
        case patientID = "patient_id"
        case therapistID = "therapist_id"
        case isEnabled = "enabled"//### "is_therapy_forced"?
    }
}

extension JSONModelSettings: Decodable {
    init(from decoder: Decoder) throws {

        // Extract the top-level values ("settings")
        let values = try decoder.container(keyedBy: CodingKeys.self)

        // Extract the settings object as a nested container
        let user = try values.nestedContainer(keyedBy: SettingsKeys.self, forKey: .settings)

        // Extract each property from the nested container
        patientID = try user.decode(String.self, forKey: .patientID)
        therapistID = try user.decode(String.self, forKey: .therapistID)

        //### decode the value for "enabled" as String
        let enabledString = try user.decode(String.self, forKey: .isEnabled)
        //### You can throw type mismatching error when `enabledString` is neither "0" or "1"
        if enabledString != "0" && enabledString != "1" {
            throw DecodingError.typeMismatch(Bool.self, DecodingError.Context(codingPath: user.codingPath + [SettingsKeys.isEnabled], debugDescription: "value for \"enabled\" needs to be \"0\" or \"1\""))
        }
        //### and convert it to Bool
        isEnabled = enabledString != "0"
    }
}