Update README.md

Removing check boxes for `Arbitrary` conformance and `OpenAPI` integration. Both of these "features" are maintained in separate libraries.

JSONAPI.podspec

@@ -16,7 +16,7 @@ Pod::Spec.new do |spec|
   #
 
   spec.name         = "JSONAPI"
-  spec.version      = "0.30.0"
+  spec.version      = "0.31.0"
   spec.summary      = "Swift Codable JSON API framework."
 
   # This description is used to generate tags and improve search results.

Package.resolved

@@ -6,8 +6,8 @@
         "repositoryURL": "https://github.com/mattpolzin/Poly.git",
         "state": {
           "branch": null,
-          "revision": "d24d4c1214dd05f89eb1182a46592856dd0a0645",
-          "version": "2.0.0"
+          "revision": "38051821d7ef49e590e26e819a2fe447e50be9ff",
+          "version": "2.0.1"
         }
       }
     ]

Package.swift

@@ -18,7 +18,7 @@ let package = Package(
 			targets: ["JSONAPITesting"])
     ],
     dependencies: [
-		.package(url: "https://github.com/mattpolzin/Poly.git", from: "2.0.0"),
+		.package(url: "https://github.com/mattpolzin/Poly.git", .upToNextMajor(from: "2.0.0")),
     ],
     targets: [
         .target(
@@ -34,5 +34,5 @@ let package = Package(
             name: "JSONAPITestingTests",
             dependencies: ["JSONAPI", "JSONAPITesting"])
     ],
-  	swiftLanguageVersions: [.version("5.1")]
+  	swiftLanguageVersions: [.v5]
 )

README.md

@@ -108,75 +108,44 @@ Note that Playground support for importing non-system Frameworks is still a bit
 #### Document
 - `data`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [x] OpenAPI
 - `included`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [x] OpenAPI
 - `errors`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [ ] OpenAPI
 - `meta`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [ ] OpenAPI
 - `jsonapi` (i.e. API Information)
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [ ] OpenAPI
 - `links`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [ ] OpenAPI
 
 #### Resource Object
 - `id`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [x] OpenAPI
 - `type`
 	- [x] Encoding/Decoding
-	- [x] OpenAPI
 - `attributes`
 	- [x] Encoding/Decoding
-	- [x] OpenAPI
 - `relationships`
 	- [x] Encoding/Decoding
-	- [x] OpenAPI
 - `links`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [ ] OpenAPI
 - `meta`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [ ] OpenAPI
 
 #### Relationship Object
 - `data`
 	- [x] Encoding/Decoding
-	- [x] Arbitrary
-	- [x] OpenAPI
 - `links`
 	- [x] Encoding/Decoding
-	- [ ] Arbitrary
-	- [ ] OpenAPI
 - `meta`
 	- [x] Encoding/Decoding
-	- [ ] Arbitrary
-	- [ ] OpenAPI
 
 #### Links Object
 - `href`
 	- [x] Encoding/Decoding
-	- [ ] Arbitrary
-	- [ ] OpenAPI
 - `meta`
 	- [x] Encoding/Decoding
-	- [ ] Arbitrary
-	- [ ] OpenAPI
 
 ### Misc
 - [x] Support transforms on `Attributes` values (e.g. to support different representations of `Date`)
@@ -194,7 +163,6 @@ Note that Playground support for importing non-system Frameworks is still a bit
 - [ ] (Maybe) Use `KeyPath` to specify `Includes` thus creating type safety around the relationship between a primary resource type and the types of included resources.
 - [ ] (Maybe) Replace `SingleResourceBody` and `ManyResourceBody` with support at the `Document` level to just interpret `PrimaryResource`, `PrimaryResource?`, or `[PrimaryResource]` as the same decoding/encoding strategies.
 - [ ] Support sideposting. JSONAPI spec might become opinionated in the future (https://github.com/json-api/json-api/pull/1197, https://github.com/json-api/json-api/issues/1215, https://github.com/json-api/json-api/issues/1216) but there is also an existing implementation to consider (https://jsonapi-suite.github.io/jsonapi_suite/ruby/writes/nested-writes). At this time, any sidepost implementation would be an awesome tertiary library to be used alongside the primary JSONAPI library. Maybe `JSONAPISideloading`.
-- [ ] Property-based testing (using `SwiftCheck`).
 - [ ] Error or warning if an included resource object is not related to a primary resource object or another included resource object (Turned off or at least not throwing by default).
 
 ## Usage
@@ -203,7 +171,7 @@ In this documentation, in order to draw attention to the difference between the
 
 ### `JSONAPI.ResourceObjectDescription`
 
-An `ResourceObjectDescription` is the `JSONAPI` framework's representation of what the **SPEC** calls a *Resource Object*. You might create the following `ResourceObjectDescription` to represent a person in a network of friends:
+A `ResourceObjectDescription` is the `JSONAPI` framework's representation of what the **SPEC** calls a *Resource Object*. You might create the following `ResourceObjectDescription` to represent a person in a network of friends:
 
 ```swift
 enum PersonDescription: IdentifiedResourceObjectDescription {
@@ -220,7 +188,7 @@ enum PersonDescription: IdentifiedResourceObjectDescription {
 }
 ```
 
-The requirements of an `ResourceObjectDescription` are:
+The requirements of a `ResourceObjectDescription` are:
 1. A static `var` "jsonType" that matches the JSON type; The **SPEC** requires every *Resource Object* to have a "type".
 2. A `struct` of `Attributes` **- OR -** `typealias Attributes = NoAttributes`
 3. A `struct` of `Relationships` **- OR -** `typealias Relationships = NoRelationships`
@@ -259,11 +227,11 @@ This readme doesn't go into detail on the **SPEC**, but the following *Resource
 
 ### `JSONAPI.ResourceObject`
 
-Once you have an `ResourceObjectDescription`, you _create_, _encode_, and _decode_ `ResourceObjects` that "fit the description". If you have a `CreatableRawIdType` (see the section on `RawIdType`s below) then you can create new `ResourceObjects` that will automatically be given unique Ids, but even without a `CreatableRawIdType` you can encode, decode and work with resource objects.
+Once you have a `ResourceObjectDescription`, you _create_, _encode_, and _decode_ `ResourceObjects` that "fit the description". If you have a `CreatableRawIdType` (see the section on `RawIdType`s below) then you can create new `ResourceObjects` that will automatically be given unique Ids, but even without a `CreatableRawIdType` you can encode, decode and work with resource objects.
 
 The `ResourceObject` and `ResourceObjectDescription` together with a `JSONAPI.Meta` type and a `JSONAPI.Links` type embody the rules and properties of a JSON API *Resource Object*.
 
-An `ResourceObject` needs to be specialized on four generic types. The first is the `ResourceObjectDescription` described above. The others are a `Meta`, `Links`, and `MaybeRawId`.
+A `ResourceObject` needs to be specialized on four generic types. The first is the `ResourceObjectDescription` described above. The others are a `Meta`, `Links`, and `MaybeRawId`.
 
 #### `Meta`
 
@@ -275,7 +243,7 @@ The third generic specialization on `ResourceObject` is `Links`. This is describ
 
 #### `MaybeRawId`
 
-The last generic specialization on `ResourceObject` is `MaybeRawId`. This is either a `RawIdType` that can be used to uniquely identify `ResourceObjects` or it is `Unidentified` which is used to indicate an `ResourceObject` does not have an `Id` (which is useful when a client is requesting that the server create an `ResourceObject` and assign it a new `Id`).
+The last generic specialization on `ResourceObject` is `MaybeRawId`. This is either a `RawIdType` that can be used to uniquely identify `ResourceObjects` or it is `Unidentified` which is used to indicate a `ResourceObject` does not have an `Id` (which is useful when a client is requesting that the server create a `ResourceObject` and assign it a new `Id`).
 
 ##### `RawIdType`
 
@@ -283,7 +251,7 @@ The raw type of `Id` to use for the `ResourceObject`. The actual `Id` of the `Re
 
 Having the `ResourceObject` type associated with the `Id` makes it easy to store all of your resource objects in a hash broken out by `ResourceObject` type; You can pass `Ids` around and always know where to look for the `ResourceObject` to which the `Id` refers. This encapsulation provides some type safety because the Ids of two `ResourceObjects` with the "raw ID" of `"1"` but different types will not compare as equal.
 
-A `RawIdType` is the underlying type that uniquely identifies an `ResourceObject`. This is often a `String` or a `UUID`.
+A `RawIdType` is the underlying type that uniquely identifies a `ResourceObject`. This is often a `String` or a `UUID`.
 
 #### Convenient `typealiases`
 
@@ -305,7 +273,7 @@ Note that I am assuming an unidentified person is a "new" person. I suspect that
 
 ### `JSONAPI.Relationships`
 
-There are two types of `Relationships`: `ToOneRelationship` and `ToManyRelationship`. An `ResourceObjectDescription`'s `Relationships` type can contain any number of `Relationship` properties of either of these types. Do not store anything other than `Relationship` properties in the `Relationships` struct of an `ResourceObjectDescription`.
+There are two types of `Relationships`: `ToOneRelationship` and `ToManyRelationship`. A `ResourceObjectDescription`'s `Relationships` type can contain any number of `Relationship` properties of either of these types. Do not store anything other than `Relationship` properties in the `Relationships` struct of a `ResourceObjectDescription`.
 
 In addition to identifying resource objects by Id and type, `Relationships` can contain `Meta` or `Links` that follow the same rules as [`Meta`](#jsonapimeta) and [`Links`](#jsonapilinks) elsewhere in the JSON API Document.
 
@@ -314,7 +282,7 @@ To describe a relationship that may be omitted (i.e. the key is not even present
 let nullableRelative: ToOneRelationship<Person?, NoMetadata, NoLinks>
 ```
 
-An resource object that does not have relationships can be described by adding the following to an `ResourceObjectDescription`:
+A `ResourceObject` that does not have relationships can be described by adding the following to a `ResourceObjectDescription`:
 ```swift
 typealias Relationships = NoRelationships
 ```
@@ -326,7 +294,7 @@ let friendIds: [Person.Identifier] = person ~> \.friends
 
 ### `JSONAPI.Attributes`
 
-The `Attributes` of an `ResourceObjectDescription` can contain any JSON encodable/decodable types as long as they are wrapped in an `Attribute`, `ValidatedAttribute`, or `TransformedAttribute` `struct`.
+The `Attributes` of a `ResourceObjectDescription` can contain any JSON encodable/decodable types as long as they are wrapped in an `Attribute`, `ValidatedAttribute`, or `TransformedAttribute` `struct`.
 
 To describe an attribute that may be omitted (i.e. the key might not even be in the JSON object), you make the entire `Attribute` optional:
 ```swift
@@ -338,7 +306,7 @@ To describe an attribute that is expected to exist but might have a `null` value
 let nullableAttribute: Attribute<String?>
 ```
 
-An resource object that does not have attributes can be described by adding the following to an `ResourceObjectDescription`:
+A resource object that does not have attributes can be described by adding the following to an `ResourceObjectDescription`:
 ```swift
 typealias Attributes = NoAttributes
 ```
@@ -396,8 +364,8 @@ public var fullName: Attribute<String> {
 
 If your computed property is wrapped in a `AttributeType` then you can still use the default subscript operator to access it (as would be the case with the `person[\.fullName]` example above). However, if you add a property to the `Attributes` `struct` that is not wrapped in an `AttributeType`, you must either access it from its full path (`person.attributes.newThing`) or with the "direct" subscript accessor (`person[direct: \.newThing]`). This keeps the subscript access unambiguous enough for the compiler to be helpful prior to explicitly casting, comparing, or storing the result.
 
-### Copying `ResourceObjects`
-`ResourceObject` is a value type, so copying is its default behavior. There are two common mutations you might want to make when copying an `ResourceObject`:
+### Copying/Mutating `ResourceObjects`
+`ResourceObject` is a value type, so copying is its default behavior. There are two common mutations you might want to make when copying a `ResourceObject`:
 1. Assigning a new `Identifier` to the copy of an identified `ResourceObject`.
 2. Assigning a new `Identifier` to the copy of an unidentified `ResourceObject`.
 
@@ -590,7 +558,7 @@ extension ResourceObjectDescription1.Attributes {
 ### Meta-Attributes
 This advanced feature may not ever be useful, but if you find yourself in the situation of dealing with an API that does not 100% follow the **SPEC** then you might find meta-attributes are just the thing to make your resource objects more natural to work with.
 
-Suppose, for example, you are presented with the unfortunate situation where a piece of information you need is only available as part of the `Id` of an resource object. Perhaps a user's `Id` is formatted "{integer}-{createdAt}" where "createdAt" is the unix timestamp when the user account was created. The following `UserDescription` will expose what you need as an attribute. Realistically, the following example code is still terrible for its error handling. Using a `Result` type and/or invariants would clean things up substantially.
+Suppose, for example, you are presented with the unfortunate situation where a piece of information you need is only available as part of the `Id` of a resource object. Perhaps a user's `Id` is formatted "{integer}-{createdAt}" where "createdAt" is the unix timestamp when the user account was created. The following `UserDescription` will expose what you need as an attribute. Realistically, the following example code is still terrible for its error handling. Using a `Result` type and/or invariants would clean things up substantially.
 
 ```swift
 enum UserDescription: ResourceObjectDescription {

Sources/JSONAPI/EmptyObjectDecoder.swift

@@ -0,0 +1,215 @@
+//
+//  EmptyObjectDecoder.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 7/2/19.
+//
+
+/// `EmptyObjectDecoder` exists internally for the sole purpose of
+/// allowing certain fallback logic paths to attempt to create `Decodable`
+/// types from empty containers (specifically in a way that is agnostic
+/// of any given encoding). In other words, this serves the same purpose
+/// as `JSONDecoder().decode(Thing.self, from: "{}".data(using: .utf8)!)`
+/// without needing to use a third party or `Foundation` library decoder.
+struct EmptyObjectDecoder: Decoder {
+
+    var codingPath: [CodingKey] = []
+
+    var userInfo: [CodingUserInfoKey : Any] = [:]
+
+    func container<Key>(keyedBy type: Key.Type) throws -> KeyedDecodingContainer<Key> where Key : CodingKey {
+        return KeyedDecodingContainer(EmptyKeyedContainer())
+    }
+
+    func unkeyedContainer() throws -> UnkeyedDecodingContainer {
+        return EmptyUnkeyedContainer()
+    }
+
+    func singleValueContainer() throws -> SingleValueDecodingContainer {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeSingleValue
+    }
+}
+
+enum EmptyObjectDecodingError: Swift.Error {
+    case emptyObjectCannotBeSingleValue
+    case emptyObjectCannotBeUnkeyedValues
+    case emptyObjectCannotHaveKeyedValues
+    case emptyObjectCannotHaveNestedContainers
+    case emptyObjectCannotHaveSuper
+}
+
+struct EmptyUnkeyedContainer: UnkeyedDecodingContainer {
+    var codingPath: [CodingKey] { return [] }
+
+    var count: Int? { return 0 }
+
+    var isAtEnd: Bool { return true }
+
+    var currentIndex: Int { return 0 }
+
+    mutating func decodeNil() throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Bool.Type) throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: String.Type) throws -> String {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Double.Type) throws -> Double {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Float.Type) throws -> Float {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int.Type) throws -> Int {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int8.Type) throws -> Int8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int16.Type) throws -> Int16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int32.Type) throws -> Int32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: Int64.Type) throws -> Int64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt.Type) throws -> UInt {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt8.Type) throws -> UInt8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt16.Type) throws -> UInt16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt32.Type) throws -> UInt32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode(_ type: UInt64.Type) throws -> UInt64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func decode<T>(_ type: T.Type) throws -> T where T : Decodable {
+        throw EmptyObjectDecodingError.emptyObjectCannotBeUnkeyedValues
+    }
+
+    mutating func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type) throws -> KeyedDecodingContainer<NestedKey> where NestedKey : CodingKey {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    mutating func nestedUnkeyedContainer() throws -> UnkeyedDecodingContainer {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    mutating func superDecoder() throws -> Decoder {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveSuper
+    }
+}
+
+struct EmptyKeyedContainer<Key: CodingKey>: KeyedDecodingContainerProtocol {
+    var codingPath: [CodingKey] { return [] }
+
+    var allKeys: [Key] { return [] }
+
+    func contains(_ key: Key) -> Bool {
+        return false
+    }
+
+    func decodeNil(forKey key: Key) throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Bool.Type, forKey key: Key) throws -> Bool {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: String.Type, forKey key: Key) throws -> String {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Double.Type, forKey key: Key) throws -> Double {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Float.Type, forKey key: Key) throws -> Float {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int.Type, forKey key: Key) throws -> Int {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int8.Type, forKey key: Key) throws -> Int8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int16.Type, forKey key: Key) throws -> Int16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int32.Type, forKey key: Key) throws -> Int32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: Int64.Type, forKey key: Key) throws -> Int64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt.Type, forKey key: Key) throws -> UInt {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt8.Type, forKey key: Key) throws -> UInt8 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt16.Type, forKey key: Key) throws -> UInt16 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt32.Type, forKey key: Key) throws -> UInt32 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode(_ type: UInt64.Type, forKey key: Key) throws -> UInt64 {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func decode<T>(_ type: T.Type, forKey key: Key) throws -> T where T : Decodable {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveKeyedValues
+    }
+
+    func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type, forKey key: Key) throws -> KeyedDecodingContainer<NestedKey> where NestedKey : CodingKey {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    func nestedUnkeyedContainer(forKey key: Key) throws -> UnkeyedDecodingContainer {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveNestedContainers
+    }
+
+    func superDecoder() throws -> Decoder {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveSuper
+    }
+
+    func superDecoder(forKey key: Key) throws -> Decoder {
+        throw EmptyObjectDecodingError.emptyObjectCannotHaveSuper
+    }
+}

Sources/JSONAPI/Resource/Attribute.swift

@@ -17,9 +17,9 @@ public protocol AttributeType: Codable {
 /// A TransformedAttribute takes a Codable type and attempts to turn it into another type.
 public struct TransformedAttribute<RawValue: Codable, Transformer: JSONAPI.Transformer>: AttributeType where Transformer.From == RawValue {
 	public let rawValue: RawValue
-
+	
 	public let value: Transformer.To
-
+	
 	public init(rawValue: RawValue) throws {
 		self.rawValue = rawValue
 		value = try Transformer.transform(rawValue)

Sources/JSONAPI/Resource/PropertyWrappers.swift

@@ -1,115 +0,0 @@
-//
-//  PropertyWrappers.swift
-//  
-//
-//  Created by Mathew Polzin on 6/20/19.
-//
-
-
-// MARK: - Transformed
-@propertyWrapper
-public struct Transformed<Transformer: JSONAPI.Transformer> {
-
-    public typealias RawValue = Transformer.From
-    public typealias Value = Transformer.To
-
-    private var _value: Value?
-
-    public var wrappedValue: Value {
-        get {
-            guard let ret = _value else {
-                fatalError("Attribute read from before initialization.")
-            }
-            return ret
-        }
-        set {
-            _value = newValue
-        }
-    }
-
-    public init(initialValue: Value, _ transformer: Transformer.Type) {
-        self._value = initialValue
-    }
-
-    public init(_ transformer: Transformer.Type) {
-        self._value = nil
-    }
-
-    public init(rawValue: RawValue, _ transformer: Transformer.Type) throws {
-        self._value = try Transformer.transform(rawValue)
-    }
-}
-
-extension Transformed: Decodable where Transformer.From: Decodable {
-    public init(from decoder: Decoder) throws {
-        let container = try decoder.singleValueContainer()
-
-        let rawVal = try container.decode(Transformer.From.self)
-
-        _value = try Transformer.transform(rawVal)
-    }
-}
-
-extension Transformed: Encodable where Transformer: ReversibleTransformer, Transformer.From: Encodable {
-    public func encode(to encoder: Encoder) throws {
-        var container = encoder.singleValueContainer()
-
-        guard let value = _value else {
-            fatalError("Attribute encoded before initialization.")
-        }
-
-        try container.encode(Transformer.reverse(value))
-    }
-}
-
-// MARK: - Nullable
-
-public protocol _Optional {
-    static var nilValue: Self { get }
-    var isNilValue: Bool { get }
-}
-
-extension Optional: _Optional {
-    public static var nilValue: Self {
-        return .none
-    }
-
-    public var isNilValue: Bool { return self == nil }
-}
-
-protocol _Nullable {}
-
-@propertyWrapper
-public struct Nullable<T: Decodable>: Decodable, _Optional, _Nullable {
-    public var wrappedValue: T?
-
-    public init(from decoder: Decoder) throws {
-        let container = try decoder.singleValueContainer()
-
-        if container.decodeNil() {
-            wrappedValue = nil
-            return
-        }
-
-        wrappedValue = try container.decode(T.self)
-    }
-
-    public init(initialValue: T? = nil) {
-        wrappedValue = initialValue
-    }
-
-    public static var nilValue: Self {
-        return .init()
-    }
-
-    public var isNilValue: Bool {
-        return wrappedValue == nil
-    }
-}
-
-extension Nullable: Encodable where T: Encodable {
-    public func encode(to encoder: Encoder) throws {
-        var container = encoder.singleValueContainer()
-        try container.encode(wrappedValue)
-    }
-}

Sources/JSONAPI/Resource/ResourceObject.swift

@@ -5,6 +5,7 @@
 //  Created by Mathew Polzin on 7/24/18.
 //
 
+
 /// A JSON API structure within an ResourceObject that contains
 /// named properties of types `ToOneRelationship` and
 /// `ToManyRelationship`.
@@ -582,7 +583,6 @@ public extension ResourceObject {
 	}
 
 	init(from decoder: Decoder) throws {
-		
 		let container = try decoder.container(keyedBy: ResourceObjectCodingKeys.self)
 		
 		let type = try container.decode(String.self, forKey: .type)
@@ -597,7 +597,9 @@ public extension ResourceObject {
 		attributes = try (NoAttributes() as? Description.Attributes) ??
 			container.decode(Description.Attributes.self, forKey: .attributes)
 
-		relationships = try (NoRelationships() as? Description.Relationships) ?? container.decode(Description.Relationships.self, forKey: .relationships)
+		relationships = try (NoRelationships() as? Description.Relationships)
+			?? container.decodeIfPresent(Description.Relationships.self, forKey: .relationships)
+			?? Description.Relationships(from: EmptyObjectDecoder())
 
 		meta = try (NoMetadata() as? MetaType) ?? container.decode(MetaType.self, forKey: .meta)
 

Tests/JSONAPITests/Attribute/AttributeTests.swift

@@ -62,70 +62,6 @@ class AttributeTests: XCTestCase {
 	}
 }
 
-// MARK: Property Wrappers
-extension AttributeTests {
-    func test_Transformed() {
-
-        struct Test: Codable {
-            @Transformed(IntToString.self)
-            var value: String = ""
-        }
-
-        let test = Test(value: "hello")
-        XCTAssertEqual(test.value, "hello")
-
-        let test2 = try! JSONDecoder().decode(Test.self,
-                                              from: #"{"value": 12}"#.data(using: .utf8)!)
-
-        XCTAssertEqual(test2.value, "12")
-        try! print(String(data: JSONEncoder().encode(test2), encoding: .utf8)!)
-
-        let test3 = try? JSONDecoder().decode(Test.self,
-                                              from: #"{"value": null}"#.data(using: .utf8)!)
-
-        XCTAssertNil(test3)
-    }
-
-    func test_Nullable() {
-        struct Test: Codable {
-            @Nullable
-            var value: String?
-        }
-
-        let test = Test(value: nil)
-        XCTAssertNil(test.value)
-
-        let test2 = Test(value: "hello")
-        XCTAssertEqual(test2.value, "hello")
-
-        let test3 = try! JSONDecoder().decode(Test.self,
-                                              from: #"{"value": "world"}"#.data(using: .utf8)!)
-
-        XCTAssertEqual(test3.value, "world")
-        try! print(String(data: JSONEncoder().encode(test2), encoding: .utf8)!)
-
-        let test4 = try? JSONDecoder().decode(Test.self,
-                                              from: #"{"value": null}"#.data(using: .utf8)!)
-
-        XCTAssertNotNil(test4)
-        XCTAssertNil(test4?.value)
-    }
-
-    func test_NullableTransformed() {
-        struct Test: Codable {
-//            Nullable<Transformed<IntToString>>
-            let x: Transformed<IntToString>
-//            @Nullable @Transformed(IdentityTransformer.self)
-            @Transformed(IntToString.self) @Nullable
-            var value: String?
-        }
-
-        let test = Test(x: .init(initialValue: "12", IntToString.self))
-
-        print(test.x.wrappedValue)
-    }
-}
-
 // MARK: Test types
 extension AttributeTests {
 	enum TestTransformer: ReversibleTransformer {
@@ -141,37 +77,12 @@ extension AttributeTests {
 		}
 	}
 
-	enum IntToString: ReversibleTransformer {
+	enum IntToString: Transformer {
 		public static func transform(_ from: Int) -> String {
 			return String(from)
 		}
-
-        public static func reverse(_ value: String) throws -> Int {
-            guard let intValue = Int(value) else {
-                fatalError("Reversed IntToString with invalid String value.")
-            }
-            return intValue
-        }
 	}
 
-    enum OptionalIntToOptionalString: ReversibleTransformer {
-        public static func transform(_ from: Int?) -> String? {
-            return from.map(String.init)
-        }
-
-        public static func reverse(_ value: String?) throws -> Int? {
-            guard let stringValue = value else {
-                return nil
-            }
-
-            guard let intValue = Int(stringValue) else {
-                fatalError("Reversed IntToString with invalid String value.")
-            }
-
-            return intValue
-        }
-    }
-
 	enum IntToInt: Transformer {
 		public static func transform(_ from: Int) -> Int {
 			return from + 100

Tests/JSONAPITests/Entity/EntityTests.swift

@@ -29,9 +29,9 @@ class EntityTests: XCTestCase {
 		let entity1 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
 		let entity = TestEntity9(attributes: .none, relationships: .init(one: entity1.pointer, nullableOne: .init(resourceObject: entity1, meta: .none, links: .none), optionalOne: .init(resourceObject: entity1, meta: .none, links: .none), optionalNullableOne: nil, optionalMany: .init(resourceObjects: [entity1, entity1], meta: .none, links: .none)), meta: .none, links: .none)
 
-		XCTAssertEqual(entity ~> \.optionalOne, Optional(entity1.id))
+		XCTAssertEqual(entity ~> \.optionalOne, entity1.id)
 	}
-	
+
 	func test_toMany_relationship_operator_access() {
 		let entity1 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
 		let entity2 = TestEntity1(attributes: .none, relationships: .none, meta: .none, links: .none)
@@ -403,6 +403,16 @@ extension EntityTests {
 								  data: entity_optional_nullable_nulled_relationship)
 	}
 
+	func test_optionalNullableRelationshipOmitted() {
+		let entity = decoded(type: TestEntity12.self,
+							 data: entity_all_relationships_optional_and_omitted)
+
+		XCTAssertNil(entity ~> \.optionalOne)
+		XCTAssertNil(entity ~> \.optionalNullableOne)
+		XCTAssertNil(entity ~> \.optionalMany)
+		XCTAssertNoThrow(try TestEntity12.check(entity))
+	}
+
 	func test_nullableRelationshipIsNull() {
 		let entity = decoded(type: TestEntity9.self,
 								   data: entity_nulled_relationship)
@@ -806,6 +816,28 @@ extension EntityTests {
 
 	typealias TestEntity11 = BasicEntity<TestEntityType11>
 
+	enum TestEntityType12: ResourceObjectDescription {
+		public static var jsonType: String { return "twelfth_test_entities" }
+
+		typealias Attributes = NoAttributes
+
+		public struct Relationships: JSONAPI.Relationships {
+			public init() {
+				optionalOne = nil
+				optionalNullableOne = nil
+				optionalMany = nil
+			}
+
+			let optionalOne: ToOneRelationship<TestEntity1, NoMetadata, NoLinks>?
+
+			let optionalNullableOne: ToOneRelationship<TestEntity1?, NoMetadata, NoLinks>?
+
+			let optionalMany: ToManyRelationship<TestEntity1, NoMetadata, NoLinks>?
+		}
+	}
+
+	typealias TestEntity12 = BasicEntity<TestEntityType12>
+
 	enum UnidentifiedTestEntityType: ResourceObjectDescription {
 		public static var jsonType: String { return "unidentified_test_entities" }
 

Tests/JSONAPITests/Entity/stubs/EntityStubs.swift

@@ -383,6 +383,16 @@ let entity_valid_validated_attribute = """
 }
 """.data(using: .utf8)!
 
+let entity_all_relationships_optional_and_omitted = """
+{
+	"id": "1",
+	"type": "twelfth_test_entities",
+	"attributes": {
+		"number": 10
+	}
+}
+""".data(using: .utf8)!
+
 let entity_unidentified = """
 {
 	"type": "unidentified_test_entities",