swift custom decoder code example

Example 1: codable custom

struct StringBacked<Value: StringRepresentable>: Codable {
    var value: Value
    
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let string = try container.decode(String.self)
        
        guard let value = Value(string) else {
            throw DecodingError.dataCorruptedError(
                in: container,
                debugDescription: """
                Failed to convert an instance of \(Value.self) from "\(string)"
                """
            )
        }
        
        self.value = value
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(value.description)
    }
}

Example 2: swift custom coding keys

struct Landmark: Codable {
    var name: String
    var foundingYear: Int
    var location: Coordinate
    var vantagePoints: [Coordinate]
    
    enum CodingKeys: String, CodingKey {
        case name = "title"
        case foundingYear = "founding_date"
        
        case location
        case vantagePoints
    }
}