StringOrValue.swift

public enum StringOrValue<Value>: Codable
where Value: Codable {

    case string(String)
    case value(Value)

    public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        do {
            self = .string(try container.decode(String.self))
        }
        catch {
            self = .value(try container.decode(Value.self))
        }
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        switch self {
        case .string(let string):
            try container.encode(string)
        case .value(let value):
            try container.encode(value)
        }
    }
}