Swiftpack.co - Package - IBM-Swift/TypeDecoder



TypeDecoder is a Swift library to allow the inspection of Swift language native and complex types. It was initially written for use within the Kitura project but can easily be used for a wide range of projects where the dynamic inspection of types is required.

Table of Contents

Swift version

The latest version of the TypeDecoder requires Swift 4.0 or newer. You can download this version of the Swift binaries by following this link. Compatibility with other Swift versions is not guaranteed.


TypeDecoder.decode() returns a TypeInfo enum which describes the type passed to decode(). The TypeInfo enum values are:

  • .single(Any.Type, Any.Type) - A basic type.
  • .keyed(Any.Type, [String: TypeInfo]) - A keyed container type, for example a struct or class.
  • .dynamicKeyed(Any.Type, key: TypeInfo, value: TypeInfo) - A dynamically keyed container type; a Dictionary.
  • .unkeyed(Any.Type, TypeInfo) - An unkeyed container type, for example an Array or Set.
  • .optional(TypeInfo) - An optional container type.
  • .cyclic(Any.Type) - A type that refers back to its own declaration, for example an Array field in a struct containing the same type as the struct.
  • .opaque(Any.Type) - A type that cannot be decoded.

For each of these enum values, the first parameter is always the original type passed to the TypeDecoder for decoding.

/// Building and running this example shows how to decode a Swift data structure.
/// You should expect to see the following output:
/// Print the returned TypeInfo and you get this:
/// StructType{
///   myString: String,
///   myOptional: Float?,
///   myCyclic: [StructType{<cyclic>}],
///   myDict: [String:Bool],
///   myArray: [Int8]
/// }
/// The Dictionary returned from decoding StructType contains:
/// ["myString": String, "myOptional": Float?, "myCyclic": [StructType{<cyclic>}], "myDict": [String:Bool], "myArray": [Int8]]
/// Each field can be individually inspected:
/// myString is type String
/// myDict is type Dictionary<String, Bool>
/// myArray contains type Int8
/// myOptional is type Float
/// Cyclics are harder to deal with as they're buried inside an Array type:
/// myCyclic is type StructType

import TypeDecoder

struct StructType: Decodable {
    let myString: String
    let myDict: Dictionary<String, Bool>
    let myArray: [Int8]
    let myOptional: Float?
    let myCyclic: [StructType]

func main() {
    do {
        let structTypeInfo = try TypeDecoder.decode(StructType.self)
        /// Print the returned TypeInfo and you get this:
        /// StructType{
        ///   myString: String,
        ///   myDict: [String:Bool],
        ///   myArray: [Int8],
        ///   myOptional: Float?,
        ///   myCyclic: [StructType{<cyclic>}]
        /// }
        print("Print the returned TypeInfo and you get this:\n\(structTypeInfo)")

        if case .keyed(_, let dict) = structTypeInfo {
            /// .keyed TypeInfo conatins a Dictionary<String, TypeInfo> of all fields contained in
            /// the keyed structure. So each field's TypeInfo can be retrieved by name.
            print("\nThe Dictionary returned from decoding StructType contains:\n\(dict)")
            print("\nEach field can be individually inspected:")

            /// Fields that are not containers will be .single
            if let theTypeInfo = dict["myString"] {
                if case .single(_) = theTypeInfo {
                    print("myString is type \(theTypeInfo)")

            /// .dynamicKeyed fields are Dictionary
            if let theTypeInfo = dict["myDict"] {
                if case .dynamicKeyed(_, let keyTypeInfo, let valueTypeInfo) = theTypeInfo {
                    print("myDict is type Dictionary<\(keyTypeInfo), \(valueTypeInfo)>")

            /// .unkeyed fields are Array or Set
            if let theTypeInfo = dict["myArray"] {
                if case .unkeyed(_, let theTypeInfo) = theTypeInfo {
                    print("myArray contains type \(theTypeInfo)")

            /// .optional field
            if let theTypeInfo = dict["myOptional"] {
                if case .optional(let theTypeInfo) = theTypeInfo {
                    print("myOptional is type \(theTypeInfo)")

            /// .cyclic fields are embedded inside .unkeyed (Array or Set)  
            if let theTypeInfo = dict["myCyclic"] {
                print("\nCyclics are harder to deal with as they're buried inside an Array type:")
                if case .unkeyed(_, let theTypeInfo) = theTypeInfo {
                    if case .cyclic(let theTypeInfo) = theTypeInfo {
                        print("myCyclic is type \(theTypeInfo)")
    } catch let error {



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1.1.0 - Jul 5, 2018

  • Update to Swift 4.1.2
  • OrderedDictionary subscript to extract value from position

1.0.0 - May 15, 2018

Initial release of typedecoder