Add convenience method for default decoding of attributes. add tests for custom decoding and encoding as well as custom coding keys. add documentation.

JSONAPI.playground/Pages/Test Library.xcplaygroundpage/Contents.swift

@@ -13,7 +13,7 @@ Please enjoy these examples, but allow me the forced casting and the lack of err
 // MARK: - Literal Expressibility
 // The JSONAPITestLib provides literal expressibility for key types to
 // make creating tests easier
-let dog = Dog(id: "1234", attributes: Dog.Attributes(name: "Buddy"), relationships: Dog.Relationships(owner: nil))
+let dog = Dog(id: "1234", attributes: Dog.Attributes(name: "Buddy"), relationships: Dog.Relationships(owner: nil), meta: .none, links: .none)
 
 // MARK: - JSON API structure checking
 // The JSONAPITestLib provides a `check` function for each Entity type

JSONAPI.playground/Pages/Usage.xcplaygroundpage/Contents.swift

@@ -13,30 +13,37 @@ let dogFromCode = try! Dog(name: "Buddy", owner: nil)
 
 typealias SingleDogDocument = JSONAPI.Document<SingleResourceBody<Dog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>
 
-let singleDogDocument = SingleDogDocument(body: SingleResourceBody(entity: dogFromCode))
+let singleDogDocument = SingleDogDocument(apiDescription: .none, body: .init(entity: dogFromCode), includes: .none, meta: .none, links: .none)
 
 let singleDogData = try! JSONEncoder().encode(singleDogDocument)
 
 // MARK: - Parse a request or response body with one Dog in it
 let dogResponse = try! JSONDecoder().decode(SingleDogDocument.self, from: singleDogData)
-let dogFromData = dogResponse.body.primaryData?.value
+let dogFromData = dogResponse.body.primaryResource?.value
+let dogOwner: Person.Identifier? = dogFromData.flatMap { $0 ~> \.owner }
+
+// MARKL - Parse a request or response body with one Dog in it using an alternative model
+typealias AltSingleDogDocument = JSONAPI.Document<SingleResourceBody<AlternativeDog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>
+let altDogResponse = try! JSONDecoder().decode(AltSingleDogDocument.self, from: singleDogData)
+let altDogFromData = altDogResponse.body.primaryResource?.value
+let altDogHuman: Person.Identifier? = altDogFromData.flatMap { $0 ~> \.human }
 
 // MARK: - Create a request or response with multiple people and dogs and houses included
 let personIds = [Person.Identifier(), Person.Identifier()]
 let dogs = try! [Dog(name: "Buddy", owner: personIds[0]), Dog(name: "Joy", owner: personIds[0]), Dog(name: "Travis", owner: personIds[1])]
-let houses = [House(), House()]
+let houses = [House(attributes: .none, relationships: .none, meta: .none, links: .none), House(attributes: .none, relationships: .none, meta: .none, links: .none)]
 let people = try! [Person(id: personIds[0], name: ["Gary", "Doe"], favoriteColor: "Orange-Red", friends: [], dogs: [dogs[0], dogs[1]], home: houses[0]), Person(id: personIds[1], name: ["Elise", "Joy"], favoriteColor: "Red", friends: [], dogs: [dogs[2]], home: houses[1])]
 
 typealias BatchPeopleDocument = JSONAPI.Document<ManyResourceBody<Person>, NoMetadata, NoLinks, Include2<Dog, House>, NoAPIDescription, UnknownJSONAPIError>
 
 let includes = dogs.map { BatchPeopleDocument.Include($0) } + houses.map { BatchPeopleDocument.Include($0) }
-let batchPeopleDocument = BatchPeopleDocument(body: .init(entities: people), includes: .init(values: includes))
+let batchPeopleDocument = BatchPeopleDocument(apiDescription: .none, body: .init(entities: people), includes: .init(values: includes), meta: .none, links: .none)
 let batchPeopleData = try! JSONEncoder().encode(batchPeopleDocument)
 
 // MARK: - Parse a request or response body with multiple people in it and dogs and houses included
 
 let peopleResponse = try! JSONDecoder().decode(BatchPeopleDocument.self, from: batchPeopleData)
-let peopleFromData = peopleResponse.body.primaryData?.values
+let peopleFromData = peopleResponse.body.primaryResource?.values
 let dogsFromData = peopleResponse.body.includes?[Dog.self]
 let housesFromData = peopleResponse.body.includes?[House.self]
 

JSONAPI.playground/Sources/Entities.swift

@@ -23,8 +23,10 @@ extension String: CreatableRawIdType {
 	}
 }
 
-// MARK: - Entity typealias for convenience
+// MARK: - typealiases for convenience
 public typealias ExampleEntity<Description: EntityDescription> = Entity<Description, NoMetadata, NoLinks, String>
+public typealias ToOne<E: Identifiable> = ToOneRelationship<E, NoMetadata, NoLinks>
+public typealias ToMany<E: Relatable> = ToManyRelationship<E, NoMetadata, NoLinks>
 
 // MARK: - A few resource objects (entities)
 public enum PersonDescription: EntityDescription {
@@ -46,11 +48,11 @@ public enum PersonDescription: EntityDescription {
 	}
 	
 	public struct Relationships: JSONAPI.Relationships {
-		public let friends: ToManyRelationship<Person>
-		public let dogs: ToManyRelationship<Dog>
-		public let home: ToOneRelationship<House>
+		public let friends: ToMany<Person>
+		public let dogs: ToMany<Dog>
+		public let home: ToOne<House>
 
-		public init(friends: ToManyRelationship<Person>, dogs: ToManyRelationship<Dog>, home: ToOneRelationship<House>) {
+		public init(friends: ToMany<Person>, dogs: ToMany<Dog>, home: ToOne<House>) {
 			self.friends = friends
 			self.dogs = dogs
 			self.home = home
@@ -62,7 +64,7 @@ public typealias Person = ExampleEntity<PersonDescription>
 
 public extension Entity where Description == PersonDescription, MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType == String {
 	public init(id: Person.Id? = nil,name: [String], favoriteColor: String, friends: [Person], dogs: [Dog], home: House) throws {
-		self = try Person(id: id ?? Person.Id(), attributes: .init(name: .init(rawValue: name), favoriteColor: .init(rawValue: favoriteColor)), relationships: .init(friends: .init(entities: friends), dogs: .init(entities: dogs), home: .init(entity: home)))
+		self = try Person(id: id ?? Person.Id(), attributes: .init(name: .init(rawValue: name), favoriteColor: .init(rawValue: favoriteColor)), relationships: .init(friends: .init(entities: friends), dogs: .init(entities: dogs), home: .init(entity: home)), meta: .none, links: .none)
 	}
 }
 
@@ -79,9 +81,9 @@ public enum DogDescription: EntityDescription {
 	}
 
 	public struct Relationships: JSONAPI.Relationships {
-		public let owner: ToOneRelationship<Person?>
+		public let owner: ToOne<Person?>
 
-		public init(owner: ToOneRelationship<Person?>) {
+		public init(owner: ToOne<Person?>) {
 			self.owner = owner
 		}
 	}
@@ -89,13 +91,41 @@ public enum DogDescription: EntityDescription {
 
 public typealias Dog = ExampleEntity<DogDescription>
 
+public enum AlternativeDogDescription: EntityDescription {
+
+	public static var type: String { return "dogs" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let name: Attribute<String>
+
+		public init(name: Attribute<String>) {
+			self.name = name
+		}
+	}
+
+	public struct Relationships: JSONAPI.Relationships {
+		public let human: ToOne<Person?>
+
+		public init(human: ToOne<Person?>) {
+			self.human = human
+		}
+
+		// define custom key mapping:
+		enum CodingKeys: String, CodingKey {
+			case human = "owner"
+		}
+	}
+}
+
+public typealias AlternativeDog = ExampleEntity<AlternativeDogDescription>
+
 public extension Entity where Description == DogDescription, MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType == String {
 	public init(name: String, owner: Person?) throws {
-		self = try Dog(attributes: .init(name: .init(rawValue: name)), relationships: DogDescription.Relationships(owner: .init(entity: owner)))
+		self = try Dog(attributes: .init(name: .init(rawValue: name)), relationships: DogDescription.Relationships(owner: .init(entity: owner)), meta: .none, links: .none)
 	}
 
 	public init(name: String, owner: Person.Id) throws {
-		self = try Dog(attributes: .init(name: .init(rawValue: name)), relationships: .init(owner: .init(id: owner)))
+		self = try Dog(attributes: .init(name: .init(rawValue: name)), relationships: .init(owner: .init(id: owner)), meta: .none, links: .none)
 	}
 }
 

Package.resolved

@@ -1,15 +1,7 @@
 {
   "object": {
     "pins": [
-      {
-        "package": "Result",
-        "repositoryURL": "https://github.com/mattpolzin/Result",
-        "state": {
-          "branch": "master",
-          "revision": "b98e238da6ea030fa7862ae6fd6500552370019c",
-          "version": null
-        }
-      }
+
     ]
   },
   "version": 1

Package.swift

@@ -14,13 +14,11 @@ let package = Package(
 			targets: ["JSONAPITestLib"])
     ],
     dependencies: [
-		// antitypical/Result without the Foundation requirement:
-        .package(url: "https://github.com/mattpolzin/Result", .branch("master"))
     ],
     targets: [
         .target(
             name: "JSONAPI",
-            dependencies: ["Result"]),
+            dependencies: []),
 		.target(
 			name: "JSONAPITestLib",
 			dependencies: ["JSONAPI"]),

README.md

@@ -52,8 +52,8 @@ Note that Playground support for importing non-system Frameworks is still a bit
 
 #### Relationship Object
 - [x] `data`
-- [ ] `links`
-- [ ] `meta`
+- [x] `links`
+- [x] `meta`
 
 #### Links Object
 - [x] `href`
@@ -67,7 +67,7 @@ Note that Playground support for importing non-system Frameworks is still a bit
 ### JSONAPITestLib
 #### Entity Validator
 - [x] Disallow optional array in `Attribute` (should be empty array, not `null`).
-- [x] Only allow `TransformedAttribute` and its derivatives within `Attributes` struct.
+- [x] Only allow `TransformedAttribute` and its derivatives as stored properties within `Attributes` struct. Computed properties can still be any type because they do not get encoded or decoded.
 - [x] Only allow `ToManyRelationship` and `ToOneRelationship` within `Relationships` struct.
 
 ### Potential Improvements
@@ -186,9 +186,11 @@ Note that I am assuming an unidentified person is a "new" person. I suspect that
 
 There are two types of `Relationships`: `ToOneRelationship` and `ToManyRelationship`. An `EntityDescription`'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 `EntityDescription`.
 
-To describe a relationship that may be omitted (i.e. the key is not even present in the JSON object), you make the entire `ToOneRelationship` or `ToManyRelationship` optional. However, this is not recommended because you can also represent optional relationships as nullable which means the key is always present. A `ToManyRelationship` can naturally represent the absence of related values with an empty array, so `ToManyRelationship` does not support nullability at all. A `ToOneRelationship` can be marked as nullable (i.e. the value might be `null` or it might be a resource identifier) like this:
+In addition to identifying entities 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.
+
+To describe a relationship that may be omitted (i.e. the key is not even present in the JSON object), you make the entire `ToOneRelationship` or `ToManyRelationship` optional. However, this is not recommended because you can also represent optional relationships as nullable which means the key is always present. A `ToManyRelationship` can naturally represent the absence of related values with an empty array, so `ToManyRelationship` does not support nullability at all. A `ToOneRelationship` can be marked as nullable (i.e. the value could be either `null` or a resource identifier) like this:
 ```
-let nullableRelative: ToOneRelationship<Person?>
+let nullableRelative: ToOneRelationship<Person?, NoMetadata, NoLinks>
 ```
 
 An entity that does not have relationships can be described by adding the following to an `EntityDescription`:
@@ -225,6 +227,11 @@ typealias Attributes = NoAttributes
 let favoriteColor: String = person[\.favoriteColor]
 ```
 
+NOTE: Because of support for computed properties that are not wrapped in `Attribute`, `TransformedAttribute`, or `ValidatedAttribute`, the compiler cannot always infer the type of thing you want back when using subscript attribute access. The following code is ambiguous about whether it should return a `String` or an `Attribute<String>`:
+```
+let favoriteColor = person[\.favoriteColor]
+```
+
 #### `Transformer`
 
 Sometimes you need to use a type that does not encode or decode itself in the way you need to represent it as a serialized JSON object. For example, the Swift `Foundation` type `Date` can encode/decode itself to `Double` out of the box, but you might want to represent dates as ISO 8601 compliant `String`s instead. The Foundation library `JSONDecoder` has a setting to make this adjustment, but for the sake of an example, you could create a `Transformer`.
@@ -263,7 +270,7 @@ You can also creator `Validators` and `ValidatedAttribute`s. A `Validator` is ju
 
 #### Computed `Attribute`
 
-You can add computed properties to your `EntityDescription.Attributes` struct if you would like to expose attributes that are not explicitly represented by the JSON. These computed properties should still have the type `Attribute` because that way you can take advantage of the quick access provided by `Entity`'s subscript operator. Here's an example of how you might take the `Person[\.name]` attribute from the example above and create a `fullName` computed property.
+You can add computed properties to your `EntityDescription.Attributes` struct if you would like to expose attributes that are not explicitly represented by the JSON. These computed properties do not have to be wrapped in `Attribute`, `ValidatedAttribute`, or `TransformedAttribute`. This allows computed attributes to be of types that are not `Codable`. Here's an example of how you might take the `Person[\.name]` attribute from the example above and create a `fullName` computed property.
 
 ```
 public var fullName: Attribute<String> {
@@ -271,6 +278,23 @@ public var fullName: Attribute<String> {
 }
 ```
 
+### Copying `Entities`
+`Entity` is a value type, so copying is its default behavior. There are two common mutations you might want to make when copying an `Entity`:
+1. Assigning a new `Identifier` to the copy of an identified `Entity`.
+2. Assigning a new `Identifier` to the copy of an unidentified `Entity`.
+
+The above can be accomplished with code like the following:
+
+```
+// use case 1
+let person1 = person.withNewIdentifier()
+
+// use case 2
+let newlyIdentifiedPerson1 = unidentifiedPerson.identified(byType: String.self)
+
+let newlyIdentifiedPerson2 = unidentifiedPerson.identified(by: "2232")
+```
+
 ### `JSONAPI.Document`
 
 The entirety of a JSON API request or response is encoded or decoded from- or to a `Document`. As an example, a JSON API response containing one `Person` and no included entities could be decoded as follows:
@@ -375,5 +399,75 @@ extension String: CreatableRawIdType {
 }
 ```
 
+### Custom Attribute or Relationship Key Mapping
+There is not anything special going on at the `JSONAPI.Attributes` and `JSONAPI.Relationships` levels, so you can easily provide custom key mappings by taking advantage of `Codable`'s `CodingKeys` pattern. Here are two models that will encode/decode equivalently but offer different naming in your codebase:
+```
+public enum EntityDescription1: JSONAPI.EntityDescription {
+	public static var type: String { return "entity" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let coolProperty: Attribute<String>
+	}
+
+	public typealias Relationships = NoRelationships
+}
+
+public enum EntityDescription2: JSONAPI.EntityDescription {
+	public static var type: String { return "entity" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let wholeOtherThing: Attribute<String>
+
+		enum CodingKeys: String, CodingKey {
+			case wholeOtherThing = "coolProperty"
+		}
+	}
+}
+```
+
+### Custom Attribute Encode/Decode
+You can safely provide your own encoding or decoding functions for your Attributes struct if you need to as long as you are careful that your encode operation correctly reverses your decode operation. Although this is generally not necessary, `AttributeType` provides a convenience method to make your decoding a bit less boilerplate ridden. This is what it looks like:
+```
+public enum EntityDescription1: JSONAPI.EntityDescription {
+	public static var type: String { return "entity" }
+
+	public struct Attributes: JSONAPI.Attributes {
+		public let property1: Attribute<String>
+		public let property2: Attribute<Int>
+		public let property3: Attribute<String>
+
+		public let weirdThing: Attribute<String>
+
+		enum CodingKeys: String, CodingKey {
+			case property1
+			case property2
+			case property3
+		}
+	}
+
+	public typealias Relationships = NoRelationships
+}
+
+extension EntityDescription1.Attributes {
+	public init(from decoder: Decoder) throws {
+		let container = try decoder.container(keyedBy: CodingKeys.self)
+
+		property1 = try .defaultDecoding(from: container, forKey: .property1)
+		property2 = try .defaultDecoding(from: container, forKey: .property2)
+		property3 = try .defaultDecoding(from: container, forKey: .property3)
+
+		weirdThing = "hello world"
+	}
+
+	public func encode(to encoder: Encoder) throws {
+		var container = encoder.container(keyedBy: CodingKeys.self)
+
+		try container.encode(property1, forKey: .property1)
+		try container.encode(property2, forKey: .property2)
+		try container.encode(property3, forKey: .property3)
+	}
+}
+```
+
 # JSONAPITestLib
 The `JSONAPI` framework is packaged with a test library to help you test your `JSONAPI` integration. The test library is called `JSONAPITestLib`. It provides literal expressibility for `Attribute`, `ToOneRelationship`, and `Id` in many situations so that you can easily write test `Entity` values into your unit tests. It also provides a `check()` function for each `Entity` type that can be used to catch problems with your `JSONAPI` structures that are not caught by Swift's type system. You can see the `JSONAPITestLib` in action in the Playground included with the `JSONAPI` repository.

Sources/JSONAPI/Document/Document.swift

@@ -66,8 +66,13 @@ public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 			guard case let .errors(errors, meta: _, links: _) = self else { return nil }
 			return errors
 		}
+
+		public var data: Data? {
+			guard case let .data(data) = self else { return nil }
+			return data
+		}
 		
-		public var primaryData: PrimaryResourceBody? {
+		public var primaryResource: PrimaryResourceBody? {
 			guard case let .data(data) = self else { return nil }
 			return data.primary
 		}
@@ -110,7 +115,7 @@ public struct Document<PrimaryResourceBody: JSONAPI.ResourceBody, MetaType: JSON
 		self.apiDescription = apiDescription
 	}
 }
-
+/*
 extension Document where IncludeType == NoIncludes {
 	public init(apiDescription: APIDescription, body: PrimaryResourceBody, meta: MetaType, links: LinksType) {
 		self.init(apiDescription: apiDescription, body: body, includes: .none, meta: meta, links: links)
@@ -182,6 +187,7 @@ extension Document where IncludeType == NoIncludes, MetaType == NoMetadata, Link
 		self.init(apiDescription: .none, body: body)
 	}
 }
+*/
 
 extension Document {
 	private enum RootCodingKeys: String, CodingKey {

Sources/JSONAPI/Document/Includes.swift

@@ -115,4 +115,11 @@ extension Includes where I: _Poly6 {
 }
 
 // MARK: - 7 includes
+public typealias Include7 = Poly7
+extension Includes where I: _Poly7 {
+	public subscript(_ lookup: I.G.Type) -> [I.G] {
+		return values.compactMap { $0.g }
+	}
+}
+
 // MARK: - 8 includes

Sources/JSONAPI/EncodingError.swift

@@ -0,0 +1,14 @@
+//
+//  EncodingError.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 12/7/18.
+//
+
+public enum JSONAPIEncodingError: Swift.Error {
+	case typeMismatch(expected: String, found: String)
+	case illegalEncoding(String)
+	case illegalDecoding(String)
+	case missingOrMalformedMetadata
+	case missingOrMalformedLinks
+}

Sources/JSONAPI/Resource/Attribute.swift

@@ -8,8 +8,10 @@
 public protocol AttributeType: Codable {
 }
 
+// MARK: TransformedAttribute
+/// 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 {
-	private let rawValue: RawValue
+	let rawValue: RawValue
 	
 	public let value: Transformer.To
 	
@@ -19,6 +21,15 @@ public struct TransformedAttribute<RawValue: Codable, Transformer: JSONAPI.Trans
 	}
 }
 
+// MARK: ValidatedAttribute
+/// A ValidatedAttribute does not transform its raw value, but it throws
+/// an error if the raw value does not match expectations.
+public typealias ValidatedAttribute<RawValue: Codable, Validator: JSONAPI.Validator> = TransformedAttribute<RawValue, Validator> where RawValue == Validator.From
+
+// MARK: Attribute
+/// An Attribute simply represents a type that can be encoded and decoded.
+public typealias Attribute<T: Codable> = TransformedAttribute<T, IdentityTransformer<T>>
+
 extension TransformedAttribute where Transformer: ReversibleTransformer {
 	public init(transformedValue: Transformer.To) throws {
 		self.value = transformedValue
@@ -43,10 +54,6 @@ extension TransformedAttribute where Transformer == IdentityTransformer<RawValue
 	}
 }
 
-public typealias ValidatedAttribute<RawValue: Codable, Validator: JSONAPI.Validator> = TransformedAttribute<RawValue, Validator> where RawValue == Validator.From
-
-public typealias Attribute<T: Codable> = TransformedAttribute<T, IdentityTransformer<T>>
-
 // MARK: - Codable
 extension TransformedAttribute {
 	public init(from decoder: Decoder) throws {
@@ -73,15 +80,15 @@ extension TransformedAttribute {
 	
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.singleValueContainer()
-		
-		// See note in decode above about the weirdness
-		// going on here.
-		let anyNil: Any? = nil
-		if let _ = anyNil as? Transformer.From,
-			(rawValue as Any?) == nil {
-			try container.encodeNil()
-		}
-		
+
 		try container.encode(rawValue)
 	}
 }
+
+// MARK: Attribute decoding and encoding defaults
+
+extension AttributeType {
+	public static func defaultDecoding<Container: KeyedDecodingContainerProtocol>(from container: Container, forKey key: Container.Key) throws -> Self {
+		return try container.decode(Self.self, forKey: key)
+	}
+}

Sources/JSONAPI/Resource/Entity.swift

@@ -8,11 +8,11 @@
 /// A JSON API structure within an Entity that contains
 /// named properties of types `ToOneRelationship` and
 /// `ToManyRelationship`.
-public typealias Relationships = Codable & Equatable
+public protocol Relationships: Codable & Equatable {}
 
 /// A JSON API structure within an Entity that contains
 /// properties of any types that are JSON encodable.
-public typealias Attributes = Codable & Equatable
+public protocol Attributes: Codable & Equatable {}
 
 /// Can be used as `Relationships` Type for Entities that do not
 /// have any Relationships.
@@ -26,23 +26,31 @@ public struct NoAttributes: Attributes {
 	public static var none: NoAttributes { return .init() }
 }
 
+/// Something that is JSONTyped provides a String representation
+/// of its type.
+public protocol JSONTyped {
+	static var type: String { get }
+}
+
+/// An `EntityProxyDescription` is an `EntityDescription`
+/// without Codable conformance.
+public protocol EntityProxyDescription: JSONTyped {
+	associatedtype Attributes: Equatable
+	associatedtype Relationships: Equatable
+}
+
 /// An `EntityDescription` describes a JSON API
 /// Resource Object. The Resource Object
 /// itself is encoded and decoded as an
 /// `Entity`, which gets specialized on an
 /// `EntityDescription`.
-public protocol EntityDescription {
-	associatedtype Attributes: JSONAPI.Attributes
-	associatedtype Relationships: JSONAPI.Relationships
-	
-	static var type: String { get }
-}
+public protocol EntityDescription: EntityProxyDescription where Attributes: JSONAPI.Attributes, Relationships: JSONAPI.Relationships {}
 
 /// EntityProxy is a protocol that can be used to create
 /// types that _act_ like Entities but cannot be encoded
 /// or decoded as Entities.
-public protocol EntityProxy: Equatable {
-	associatedtype Description: EntityDescription
+public protocol EntityProxy: Equatable, JSONTyped {
+	associatedtype Description: EntityProxyDescription
 	associatedtype EntityRawIdType: JSONAPI.MaybeRawId
 
 	typealias Id = JSONAPI.Id<EntityRawIdType, Self>
@@ -71,7 +79,9 @@ extension EntityProxy {
 /// EntityType is the protocol that Entity conforms to. This
 /// protocol lets other types accept any Entity as a generic
 /// specialization.
-public protocol EntityType: EntityProxy, PrimaryResource {
+public protocol EntityType: EntityProxy, PrimaryResource where Description: EntityDescription {
+	associatedtype Meta: JSONAPI.Meta
+	associatedtype Links: JSONAPI.Links
 }
 
 public protocol IdentifiableEntityType: EntityType, Relatable where EntityRawIdType: JSONAPI.RawIdType {}
@@ -81,6 +91,10 @@ public protocol IdentifiableEntityType: EntityType, Relatable where EntityRawIdT
 /// "Resource Object."
 /// See https://jsonapi.org/format/#document-resource-objects
 public struct Entity<Description: JSONAPI.EntityDescription, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links, EntityRawIdType: JSONAPI.MaybeRawId>: EntityType {
+
+	public typealias Meta = MetaType
+	public typealias Links = LinksType
+
 	/// The `Entity`'s Id. This can be of type `Unidentified` if
 	/// the entity is being created clientside and the
 	/// server is being asked to create a unique Id. Otherwise,
@@ -108,9 +122,8 @@ public struct Entity<Description: JSONAPI.EntityDescription, MetaType: JSONAPI.M
 	}
 }
 
-extension Entity: IdentifiableEntityType, Relatable, WrappedRelatable where EntityRawIdType: JSONAPI.RawIdType {
+extension Entity: Identifiable, IdentifiableEntityType, Relatable where EntityRawIdType: JSONAPI.RawIdType {
 	public typealias Identifier = Entity.Id
-	public typealias WrappedIdentifier = Identifier
 }
 
 extension Entity: CustomStringConvertible {
@@ -140,6 +153,7 @@ extension Entity where EntityRawIdType == Unidentified {
 	}
 }
 
+/*
 extension Entity where Description.Attributes == NoAttributes {
 	public init(id: Entity.Id, relationships: Description.Relationships, meta: MetaType, links: LinksType) {
 		self.init(id: id, attributes: NoAttributes(), relationships: relationships, meta: meta, links: links)
@@ -326,6 +340,12 @@ extension Entity where MetaType == NoMetadata, EntityRawIdType: CreatableRawIdTy
 	}
 }
 
+extension Entity where MetaType == NoMetadata, EntityRawIdType == Unidentified {
+	public init(attributes: Description.Attributes, relationships: Description.Relationships, links: LinksType) {
+		self.init(attributes: attributes, relationships: relationships, meta: .none, links: links)
+	}
+}
+
 extension Entity where LinksType == NoLinks {
 	public init(id: Entity.Id, attributes: Description.Attributes, relationships: Description.Relationships, meta: MetaType) {
 		self.init(id: id, attributes: attributes, relationships: relationships, meta: meta, links: .none)
@@ -338,6 +358,12 @@ extension Entity where LinksType == NoLinks, EntityRawIdType: CreatableRawIdType
 	}
 }
 
+extension Entity where LinksType == NoLinks, EntityRawIdType == Unidentified {
+	public init(attributes: Description.Attributes, relationships: Description.Relationships, meta: MetaType) {
+		self.init(attributes: attributes, relationships: relationships, meta: meta, links: .none)
+	}
+}
+
 extension Entity where MetaType == NoMetadata, LinksType == NoLinks {
 	public init(id: Entity.Id, attributes: Description.Attributes, relationships: Description.Relationships) {
 		self.init(id: id, attributes: attributes, relationships: relationships, meta: .none, links: .none)
@@ -350,12 +376,55 @@ extension Entity where MetaType == NoMetadata, LinksType == NoLinks, EntityRawId
 	}
 }
 
+extension Entity where MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType == Unidentified {
+	public init(attributes: Description.Attributes, relationships: Description.Relationships) {
+		self.init(attributes: attributes, relationships: relationships, meta: .none, links: .none)
+	}
+}
+*/
+
 // MARK: Pointer for Relationships use.
 public extension Entity where EntityRawIdType: JSONAPI.RawIdType {
+
+	/// An Entity.Pointer is a `ToOneRelationship` with no metadata or links.
+	/// This is just a convenient way to reference an Entity so that
+	/// other Entities' Relationships can be built up from it.
+	public typealias Pointer = ToOneRelationship<Entity, NoMetadata, NoLinks>
+
+	/// Entity.Pointers is a `ToManyRelationship` with no metadata or links.
+	/// This is just a convenient way to reference a bunch of Entities so
+	/// that other Entities' Relationships can be built up from them.
+	public typealias Pointers = ToManyRelationship<Entity, NoMetadata, NoLinks>
+
 	/// Get a pointer to this entity that can be used as a
 	/// relationship to another entity.
-	public var pointer: ToOneRelationship<Entity> {
-		return ToOneRelationship(entity: self)
+	public var pointer: Pointer {
+		return Pointer(entity: self)
+	}
+
+	public func pointer<MType: JSONAPI.Meta, LType: JSONAPI.Links>(withMeta meta: MType, links: LType) -> ToOneRelationship<Entity, MType, LType> {
+		return ToOneRelationship(entity: self, meta: meta, links: links)
+	}
+}
+
+// MARK: Identifying Unidentified Entities
+public extension Entity where EntityRawIdType == Unidentified {
+	/// Create a new Entity from this one with a newly created
+	/// unique Id of the given type.
+	public func identified<RawIdType: CreatableRawIdType>(byType: RawIdType.Type) -> Entity<Description, MetaType, LinksType, RawIdType> {
+		return .init(attributes: attributes, relationships: relationships, meta: meta, links: links)
+	}
+
+	/// Create a new Entity from this one with the given Id.
+	public func identified<RawIdType: JSONAPI.RawIdType>(by id: RawIdType) -> Entity<Description, MetaType, LinksType, RawIdType> {
+		return .init(id: Entity<Description, MetaType, LinksType, RawIdType>.Identifier(rawValue: id), attributes: attributes, relationships: relationships, meta: meta, links: links)
+	}
+}
+
+public extension Entity where EntityRawIdType: CreatableRawIdType {
+	/// Create a copy of this Entity with a new unique Id.
+	public func withNewIdentifier() -> Entity {
+		return Entity(attributes: attributes, relationships: relationships, meta: meta, links: links)
 	}
 }
 
@@ -379,8 +448,19 @@ public extension EntityProxy {
 	/// allows you to write `entity[\.propertyName]` instead
 	/// of `entity.relationships.propertyName`.
 	subscript<T, TFRM: Transformer, U>(_ path: KeyPath<Description.Attributes, TransformedAttribute<T, TFRM>?>) -> U? where TFRM.To == U? {
+		// Implementation Note: Handles Transform that returns optional
+		// type.
 		return attributes[keyPath: path].flatMap { $0.value }
 	}
+
+	/// Access the computed attribute at the given keypath. This just
+	/// allows you to write `entity[\.propertyName]` instead
+	/// of `entity.relationships.propertyName`.
+	subscript<T>(_ path: KeyPath<Description.Attributes, T>) -> T {
+		// Implementation Note: Handles attributes that are not
+		// AttributeType. These should only exist as computed properties.
+		return attributes[keyPath: path]
+	}
 }
 
 // MARK: Relationship Access
@@ -388,16 +468,41 @@ public extension EntityProxy {
 	/// Access to an Id of a `ToOneRelationship`.
 	/// This allows you to write `entity ~> \.other` instead
 	/// of `entity.relationships.other.id`.
-	public static func ~><OtherEntity: OptionalRelatable>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity>>) -> OtherEntity.WrappedIdentifier {
+	public static func ~><OtherEntity: Identifiable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity, MType, LType>>) -> OtherEntity.Identifier {
 		return entity.relationships[keyPath: path].id
 	}
 
+	/// Access to an Id of an optional `ToOneRelationship`.
+	/// This allows you to write `entity ~> \.other` instead
+	/// of `entity.relationships.other?.id`.
+	public static func ~><OtherEntity: OptionalRelatable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity, MType, LType>?>) -> OtherEntity.Identifier {
+		// Implementation Note: This signature applies to `ToOneRelationship<E?, _, _>?`
+		// whereas the one below applies to `ToOneRelationship<E, _, _>?`
+		return entity.relationships[keyPath: path]?.id
+	}
+
+	/// Access to an Id of an optional `ToOneRelationship`.
+	/// This allows you to write `entity ~> \.other` instead
+	/// of `entity.relationships.other?.id`.
+	public static func ~><OtherEntity: Relatable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToOneRelationship<OtherEntity, MType, LType>?>) -> OtherEntity.Identifier? {
+		// Implementation Note: This signature applies to `ToOneRelationship<E, _, _>?`
+		// whereas the one above applies to `ToOneRelationship<E?, _, _>?`
+		return entity.relationships[keyPath: path]?.id
+	}
+
 	/// Access to all Ids of a `ToManyRelationship`.
 	/// This allows you to write `entity ~> \.others` instead
 	/// of `entity.relationships.others.ids`.
-	public static func ~><OtherEntity: Relatable>(entity: Self, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity>>) -> [OtherEntity.Identifier] {
+	public static func ~><OtherEntity: Relatable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity, MType, LType>>) -> [OtherEntity.Identifier] {
 		return entity.relationships[keyPath: path].ids
 	}
+
+	/// Access to all Ids of an optional `ToManyRelationship`.
+	/// This allows you to write `entity ~> \.others` instead
+	/// of `entity.relationships.others?.ids`.
+	public static func ~><OtherEntity: Relatable, MType: JSONAPI.Meta, LType: JSONAPI.Links>(entity: Self, path: KeyPath<Description.Relationships, ToManyRelationship<OtherEntity, MType, LType>?>) -> [OtherEntity.Identifier]? {
+		return entity.relationships[keyPath: path]?.ids
+	}
 }
 
 infix operator ~>
@@ -451,9 +556,10 @@ public extension Entity {
 
 		let maybeUnidentified = Unidentified() as? EntityRawIdType
 		id = try maybeUnidentified.map { Entity.Id(rawValue: $0) } ?? container.decode(Entity.Id.self, forKey: .id)
-		
-		attributes = try (NoAttributes() as? Description.Attributes) ?? container.decode(Description.Attributes.self, forKey: .attributes)
-		
+
+		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)
 
 		meta = try (NoMetadata() as? MetaType) ?? container.decode(MetaType.self, forKey: .meta)

Sources/JSONAPI/Resource/Id.swift

@@ -34,13 +34,31 @@ public struct Unidentified: MaybeRawId, CustomStringConvertible {
 	public var description: String { return "Unidentified" }
 }
 
-public protocol MaybeId: Codable {
-	associatedtype EntityType: JSONAPI.EntityProxy
+public protocol OptionalId: Codable {
+	associatedtype IdentifiableType: JSONAPI.JSONTyped
 	associatedtype RawType: MaybeRawId
+
+	var rawValue: RawType { get }
+	init(rawValue: RawType)
 }
 
-public protocol IdType: MaybeId, CustomStringConvertible, Hashable where RawType: RawIdType {
-	var rawValue: RawType { get }
+public protocol IdType: OptionalId, CustomStringConvertible, Hashable where RawType: RawIdType {}
+
+extension Optional: MaybeRawId where Wrapped: Codable & Equatable {}
+extension Optional: OptionalId where Wrapped: IdType {
+	public typealias IdentifiableType = Wrapped.IdentifiableType
+	public typealias RawType = Wrapped.RawType?
+
+	public var rawValue: Wrapped.RawType? {
+		guard case .some(let value) = self else {
+			return nil
+		}
+		return value.rawValue
+	}
+
+	public init(rawValue: Wrapped.RawType?) {
+		self = rawValue.map { Wrapped(rawValue: $0) }
+	}
 }
 
 public extension IdType {
@@ -53,7 +71,7 @@ public protocol CreatableIdType: IdType {
 
 /// An Entity ID. These IDs can be encoded to or decoded from
 /// JSON API IDs.
-public struct Id<RawType: MaybeRawId, EntityType: JSONAPI.EntityProxy>: Codable, Equatable, MaybeId {
+public struct Id<RawType: MaybeRawId, IdentifiableType: JSONAPI.JSONTyped>: Equatable, OptionalId {
 
 	public let rawValue: RawType
 	
@@ -63,7 +81,8 @@ public struct Id<RawType: MaybeRawId, EntityType: JSONAPI.EntityProxy>: Codable,
 
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.singleValueContainer()
-		rawValue = try container.decode(RawType.self)
+		let rawValue = try container.decode(RawType.self)
+		self.init(rawValue: rawValue)
 	}
 
 	public func encode(to encoder: Encoder) throws {
@@ -72,7 +91,11 @@ public struct Id<RawType: MaybeRawId, EntityType: JSONAPI.EntityProxy>: Codable,
 	}
 }
 
-extension Id: Hashable, CustomStringConvertible, IdType where RawType: RawIdType {}
+extension Id: Hashable, CustomStringConvertible, IdType where RawType: RawIdType {
+	public static func id(from rawValue: RawType) -> Id<RawType, IdentifiableType> {
+		return Id(rawValue: rawValue)
+	}
+}
 
 extension Id: CreatableIdType where RawType: CreatableRawIdType {
 	public init() {

Sources/JSONAPI/Resource/Poly.swift

@@ -5,8 +5,6 @@
 //  Created by Mathew Polzin on 11/22/18.
 //
 
-import Result
-
 /// Poly is a protocol to which types that
 /// are polymorphic belong to. Specifically,
 /// Poly1, Poly2, Poly3, etc. types conform
@@ -28,7 +26,7 @@ private func decode<Entity: JSONAPI.EntityType>(_ type: Entity.Type, from contai
 	} catch (let err) {
 		ret = .failure(DecodingError.typeMismatch(Entity.Description.self,
 												  .init(codingPath: container.codingPath,
-														debugDescription: err.localizedDescription,
+														debugDescription: String(describing: err),
 														underlyingError: err)))
 	}
 	return ret
@@ -646,3 +644,158 @@ extension Poly6: CustomStringConvertible {
 		return "Poly(\(str))"
 	}
 }
+
+// MARK: - 7 types
+public protocol _Poly7: _Poly6 {
+	associatedtype G: EntityType
+	var g: G? { get }
+
+	init(_ g: G)
+}
+
+public extension _Poly7 {
+	subscript(_ lookup: G.Type) -> G? {
+		return g
+	}
+}
+
+public enum Poly7<A: EntityType, B: EntityType, C: EntityType, D: EntityType, E: EntityType, F: EntityType, G: EntityType>: _Poly7 {
+	case a(A)
+	case b(B)
+	case c(C)
+	case d(D)
+	case e(E)
+	case f(F)
+	case g(G)
+
+	public var a: A? {
+		guard case let .a(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ a: A) {
+		self = .a(a)
+	}
+
+	public var b: B? {
+		guard case let .b(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ b: B) {
+		self = .b(b)
+	}
+
+	public var c: C? {
+		guard case let .c(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ c: C) {
+		self = .c(c)
+	}
+
+	public var d: D? {
+		guard case let .d(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ d: D) {
+		self = .d(d)
+	}
+
+	public var e: E? {
+		guard case let .e(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ e: E) {
+		self = .e(e)
+	}
+
+	public var f: F? {
+		guard case let .f(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ f: F) {
+		self = .f(f)
+	}
+
+	public var g: G? {
+		guard case let .g(ret) = self else { return nil }
+		return ret
+	}
+
+	public init(_ g: G) {
+		self = .g(g)
+	}
+
+	public init(from decoder: Decoder) throws {
+		let container = try decoder.singleValueContainer()
+
+		let attempts = [
+			try decode(A.self, from: container).map { Poly7.a($0) },
+			try decode(B.self, from: container).map { Poly7.b($0) },
+			try decode(C.self, from: container).map { Poly7.c($0) },
+			try decode(D.self, from: container).map { Poly7.d($0) },
+			try decode(E.self, from: container).map { Poly7.e($0) },
+			try decode(F.self, from: container).map { Poly7.f($0) },
+			try decode(G.self, from: container).map { Poly7.g($0) }]
+
+		let maybeVal: Poly7<A, B, C, D, E, F, G>? = attempts
+			.compactMap { $0.value }
+			.first
+
+		guard let val = maybeVal else {
+			throw EncodingError.invalidValue(Poly7<A, B, C, D, E, F, G>.self, .init(codingPath: decoder.codingPath, debugDescription: "Failed to find an include of the expected type. Attempts: \(attempts.map { $0.error }.compactMap { $0 })"))
+		}
+
+		self = val
+	}
+
+	public func encode(to encoder: Encoder) throws {
+		var container = encoder.singleValueContainer()
+
+		switch self {
+		case .a(let a):
+			try container.encode(a)
+		case .b(let b):
+			try container.encode(b)
+		case .c(let c):
+			try container.encode(c)
+		case .d(let d):
+			try container.encode(d)
+		case .e(let e):
+			try container.encode(e)
+		case .f(let f):
+			try container.encode(f)
+		case .g(let g):
+			try container.encode(g)
+		}
+	}
+}
+
+extension Poly7: CustomStringConvertible {
+	public var description: String {
+		let str: String
+		switch self {
+		case .a(let a):
+			str = String(describing: a)
+		case .b(let b):
+			str = String(describing: b)
+		case .c(let c):
+			str = String(describing: c)
+		case .d(let d):
+			str = String(describing: d)
+		case .e(let e):
+			str = String(describing: e)
+		case .f(let f):
+			str = String(describing: f)
+		case .g(let g):
+			str = String(describing: g)
+		}
+
+		return "Poly(\(str))"
+	}
+}

Sources/JSONAPI/Resource/Relationship.swift

@@ -5,30 +5,59 @@
 //  Created by Mathew Polzin on 8/31/18.
 //
 
-public protocol RelationshipType: Codable {}
+public protocol RelationshipType {
+	associatedtype LinksType
+	associatedtype MetaType
+
+	var links: LinksType { get }
+	var meta: MetaType { get }
+}
 
 /// An Entity relationship that can be encoded to or decoded from
 /// a JSON API "Resource Linkage."
 /// See https://jsonapi.org/format/#document-resource-object-linkage
 /// A convenient typealias might make your code much more legible: `One<EntityDescription>`
-public struct ToOneRelationship<Relatable: JSONAPI.OptionalRelatable>: RelationshipType, Equatable {
+public struct ToOneRelationship<Identifiable: JSONAPI.Identifiable, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links>: RelationshipType, Equatable {
 
-	public let id: Relatable.WrappedIdentifier
+	public let id: Identifiable.Identifier
 
-	public init(id: Relatable.WrappedIdentifier) {
+	public let meta: MetaType
+	public let links: LinksType
+
+	public init(id: Identifiable.Identifier, meta: MetaType, links: LinksType) {
 		self.id = id
+		self.meta = meta
+		self.links = links
 	}
 }
 
-extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier {
-	public init<E: EntityType>(entity: E) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
-		id = entity.id
+extension ToOneRelationship where MetaType == NoMetadata, LinksType == NoLinks {
+	public init(id: Identifiable.Identifier) {
+		self.init(id: id, meta: .none, links: .none)
 	}
 }
 
-extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Identifier? {
-	public init<E: EntityType>(entity: E?) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
-		id = entity?.id
+extension ToOneRelationship {
+	public init<E: EntityType>(entity: E, meta: MetaType, links: LinksType) where E.Id == Identifiable.Identifier {
+		self.init(id: entity.id, meta: meta, links: links)
+	}
+}
+
+extension ToOneRelationship where MetaType == NoMetadata, LinksType == NoLinks {
+	public init<E: EntityType>(entity: E) where E.Id == Identifiable.Identifier {
+		self.init(id: entity.id, meta: .none, links: .none)
+	}
+}
+
+extension ToOneRelationship where Identifiable: OptionalRelatable {
+	public init<E: EntityType>(entity: E?, meta: MetaType, links: LinksType) where E.Id == Identifiable.Wrapped.Identifier {
+		self.init(id: entity?.id, meta: meta, links: links)
+	}
+}
+
+extension ToOneRelationship where Identifiable: OptionalRelatable, MetaType == NoMetadata, LinksType == NoLinks {
+	public init<E: EntityType>(entity: E?) where E.Id == Identifiable.Wrapped.Identifier {
+		self.init(id: entity?.id, meta: .none, links: .none)
 	}
 }
 
@@ -36,73 +65,105 @@ extension ToOneRelationship where Relatable.WrappedIdentifier == Relatable.Ident
 /// a JSON API "Resource Linkage."
 /// See https://jsonapi.org/format/#document-resource-object-linkage
 /// A convenient typealias might make your code much more legible: `Many<EntityDescription>`
-public struct ToManyRelationship<Relatable: JSONAPI.Relatable>: RelationshipType, Equatable {
+public struct ToManyRelationship<Relatable: JSONAPI.Relatable, MetaType: JSONAPI.Meta, LinksType: JSONAPI.Links>: RelationshipType, Equatable {
 
 	public let ids: [Relatable.Identifier]
 
-	public init(ids: [Relatable.Identifier]) {
+	public let meta: MetaType
+	public let links: LinksType
+
+	public init(ids: [Relatable.Identifier], meta: MetaType, links: LinksType) {
 		self.ids = ids
+		self.meta = meta
+		self.links = links
 	}
 
-	public init<T: JSONAPI.Relatable>(relationships: [ToOneRelationship<T>]) where T.WrappedIdentifier == Relatable.Identifier {
-		ids = relationships.map { $0.id }
+	public init<T: JSONAPI.Identifiable>(pointers: [ToOneRelationship<T, NoMetadata, NoLinks>], meta: MetaType, links: LinksType) where T.Identifier == Relatable.Identifier {
+		ids = pointers.map { $0.id }
+		self.meta = meta
+		self.links = links
 	}
 
-	private init() {
-		ids = []
+	public init<E: EntityType>(entities: [E], meta: MetaType, links: LinksType) where E.Id == Relatable.Identifier {
+		self.init(ids: entities.map { $0.id }, meta: meta, links: links)
 	}
-	
+
+	private init(meta: MetaType, links: LinksType) {
+		self.init(ids: [], meta: meta, links: links)
+	}
+
+	public static func none(withMeta meta: MetaType, links: LinksType) -> ToManyRelationship {
+		return ToManyRelationship(meta: meta, links: links)
+	}
+}
+
+extension ToManyRelationship where MetaType == NoMetadata, LinksType == NoLinks {
+
+	public init(ids: [Relatable.Identifier]) {
+		self.init(ids: ids, meta: .none, links: .none)
+	}
+
+	public init<T: JSONAPI.Identifiable>(pointers: [ToOneRelationship<T, NoMetadata, NoLinks>]) where T.Identifier == Relatable.Identifier {
+		self.init(pointers: pointers, meta: .none, links: .none)
+	}
+
 	public static var none: ToManyRelationship {
-		return .init()
+		return .none(withMeta: .none, links: .none)
+	}
+
+	public init<E: EntityType>(entities: [E]) where E.Id == Relatable.Identifier {
+		self.init(entities: entities, meta: .none, links: .none)
 	}
 }
 
-extension ToManyRelationship {
-	public init<E: EntityType>(entities: [E]) where E.Description == Relatable.Description, E.Id == Relatable.Identifier {
-		ids = entities.map { $0.id }
-	}
+public protocol Identifiable: JSONTyped {
+	associatedtype Identifier: Equatable
 }
 
-/// The WrappedRelatable (a.k.a OptionalRelatable) protocol
-/// describes Optional<T: Relatable> and Relatable types.
-public protocol WrappedRelatable: Codable, Equatable {
-	associatedtype Description: EntityDescription
-	associatedtype Identifier: JSONAPI.IdType
-	associatedtype WrappedIdentifier: Codable, Equatable
-}
-public typealias OptionalRelatable = WrappedRelatable
-
 /// The Relatable protocol describes anything that
 /// has an IdType Identifier
-public protocol Relatable: WrappedRelatable {}
+public protocol Relatable: Identifiable where Identifier: JSONAPI.IdType {
+}
 
-extension Optional: OptionalRelatable where Wrapped: Relatable {
-	public typealias Description = Wrapped.Description
-	public typealias Identifier = Wrapped.Identifier
-	public typealias WrappedIdentifier = Identifier?
+/// OptionalRelatable just describes an Optional
+/// with a Reltable Wrapped type.
+public protocol OptionalRelatable: Identifiable where Identifier == Wrapped.Identifier? {
+	associatedtype Wrapped: JSONAPI.Relatable
+}
+
+extension Optional: Identifiable, OptionalRelatable, JSONTyped where Wrapped: JSONAPI.Relatable {
+	public typealias Identifier = Wrapped.Identifier?
+
+	public static var type: String { return Wrapped.type }
 }
 
 // MARK: Codable
 private enum ResourceLinkageCodingKeys: String, CodingKey {
 	case data = "data"
+	case meta = "meta"
+	case links = "links"
 }
 private enum ResourceIdentifierCodingKeys: String, CodingKey {
 	case id = "id"
 	case entityType = "type"
 }
 
-public enum JSONAPIEncodingError: Swift.Error {
-	case typeMismatch(expected: String, found: String)
-	case illegalEncoding(String)
-	case illegalDecoding(String)
-	case missingOrMalformedMetadata
-	case missingOrMalformedLinks
-}
-
-extension ToOneRelationship {
+extension ToOneRelationship: Codable where Identifiable.Identifier: OptionalId {
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.container(keyedBy: ResourceLinkageCodingKeys.self)
 
+		if let noMeta = NoMetadata() as? MetaType {
+			meta = noMeta
+		} else {
+			meta = try container.decode(MetaType.self, forKey: .meta)
+		}
+
+		if let noLinks = NoLinks() as? LinksType {
+			links = noLinks
+		} else {
+			links = try container.decode(LinksType.self, forKey: .links)
+		}
+
 		// A little trickery follows. If the id is nil, the
 		// container.decode(Identifier.self) will fail even if Identifier
 		// is Optional. However, we can check if decoding nil
@@ -110,7 +171,7 @@ extension ToOneRelationship {
 		// type at which point we can store nil in `id`.
 		let anyNil: Any? = nil
 		if try container.decodeNil(forKey: .data),
-			let val = anyNil as? Relatable.WrappedIdentifier {
+			let val = anyNil as? Identifiable.Identifier {
 			id = val
 			return
 		}
@@ -119,11 +180,11 @@ extension ToOneRelationship {
 		
 		let type = try identifier.decode(String.self, forKey: .entityType)
 		
-		guard type == Relatable.Description.type else {
-			throw JSONAPIEncodingError.typeMismatch(expected: Relatable.Description.type, found: type)
+		guard type == Identifiable.type else {
+			throw JSONAPIEncodingError.typeMismatch(expected: Identifiable.type, found: type)
 		}
 		
-		id = try identifier.decode(Relatable.WrappedIdentifier.self, forKey: .id)
+		id = Identifiable.Identifier(rawValue: try identifier.decode(Identifiable.Identifier.RawType.self, forKey: .id))
 	}
 	
 	public func encode(to encoder: Encoder) throws {
@@ -133,17 +194,46 @@ extension ToOneRelationship {
 			try container.encodeNil(forKey: .data)
 		}
 
+		if MetaType.self != NoMetadata.self {
+			try container.encode(meta, forKey: .meta)
+		}
+
+		if LinksType.self != NoLinks.self {
+			try container.encode(links, forKey: .links)
+		}
+
+		// If id is nil, instead of {id: , type: } we will just
+		// encode `null`
+		let anyNil: Any? = nil
+		let nilId = anyNil as? Identifiable.Identifier
+		guard id != nilId else {
+			try container.encodeNil(forKey: .data)
+			return
+		}
+
 		var identifier = container.nestedContainer(keyedBy: ResourceIdentifierCodingKeys.self, forKey: .data)
 		
-		try identifier.encode(id, forKey: .id)
-		try identifier.encode(Relatable.Description.type, forKey: .entityType)
+		try identifier.encode(id.rawValue, forKey: .id)
+		try identifier.encode(Identifiable.type, forKey: .entityType)
 	}
 }
 
-extension ToManyRelationship {
+extension ToManyRelationship: Codable {
 	public init(from decoder: Decoder) throws {
 		let container = try decoder.container(keyedBy: ResourceLinkageCodingKeys.self)
-		
+
+		if let noMeta = NoMetadata() as? MetaType {
+			meta = noMeta
+		} else {
+			meta = try container.decode(MetaType.self, forKey: .meta)
+		}
+
+		if let noLinks = NoLinks() as? LinksType {
+			links = noLinks
+		} else {
+			links = try container.decode(LinksType.self, forKey: .links)
+		}
+
 		var identifiers = try container.nestedUnkeyedContainer(forKey: .data)
 		
 		var newIds = [Relatable.Identifier]()
@@ -152,24 +242,33 @@ extension ToManyRelationship {
 			
 			let type = try identifier.decode(String.self, forKey: .entityType)
 			
-			guard type == Relatable.Description.type else {
-				throw JSONAPIEncodingError.typeMismatch(expected: Relatable.Description.type, found: type)
+			guard type == Relatable.type else {
+				throw JSONAPIEncodingError.typeMismatch(expected: Relatable.type, found: type)
 			}
 			
-			newIds.append(try identifier.decode(Relatable.Identifier.self, forKey: .id))
+			newIds.append(Relatable.Identifier(rawValue: try identifier.decode(Relatable.Identifier.RawType.self, forKey: .id)))
 		}
 		ids = newIds
 	}
 	
 	public func encode(to encoder: Encoder) throws {
 		var container = encoder.container(keyedBy: ResourceLinkageCodingKeys.self)
+
+		if MetaType.self != NoMetadata.self {
+			try container.encode(meta, forKey: .meta)
+		}
+
+		if LinksType.self != NoLinks.self {
+			try container.encode(links, forKey: .links)
+		}
+
 		var identifiers = container.nestedUnkeyedContainer(forKey: .data)
 		
 		for id in ids {
 			var identifier = identifiers.nestedContainer(keyedBy: ResourceIdentifierCodingKeys.self)
 			
-			try identifier.encode(id, forKey: .id)
-			try identifier.encode(Relatable.Description.type, forKey: .entityType)
+			try identifier.encode(id.rawValue, forKey: .id)
+			try identifier.encode(Relatable.type, forKey: .entityType)
 		}
 	}
 }

Sources/JSONAPI/Result.swift

@@ -0,0 +1,45 @@
+//
+//  Result.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 12/5/18.
+//
+
+enum Result<T, E: Swift.Error> {
+	case success(T)
+	case failure(E)
+
+	var value: T? {
+		guard case .success(let val) = self else {
+			return nil
+		}
+		return val
+	}
+
+	var error: E? {
+		guard case .failure(let err) = self else {
+			return nil
+		}
+		return err
+	}
+
+	func map<U>(_ transform: (T) -> U) -> Result<U, E> {
+		switch self {
+		case .failure(let err):
+			return .failure(err)
+		case .success(let val):
+			return .success(transform(val))
+		}
+	}
+}
+
+extension Result: CustomStringConvertible where T: CustomStringConvertible, E: CustomStringConvertible {
+	var description: String {
+		switch self {
+		case .success(let val):
+			return String(describing: val)
+		case .failure(let err):
+			return String(describing: err)
+		}
+	}
+}

Sources/JSONAPITestLib/Attribute+Literal.swift

@@ -39,6 +39,14 @@ extension TransformedAttribute: ExpressibleByFloatLiteral where RawValue: Expres
 	}
 }
 
+extension Optional: ExpressibleByFloatLiteral where Wrapped: ExpressibleByFloatLiteral {
+	public typealias FloatLiteralType = Wrapped.FloatLiteralType
+
+	public init(floatLiteral value: FloatLiteralType) {
+		self = .some(Wrapped(floatLiteral: value))
+	}
+}
+
 extension TransformedAttribute: ExpressibleByBooleanLiteral where RawValue: ExpressibleByBooleanLiteral, Transformer == IdentityTransformer<RawValue> {
 	public typealias BooleanLiteralType = RawValue.BooleanLiteralType
 
@@ -47,6 +55,14 @@ extension TransformedAttribute: ExpressibleByBooleanLiteral where RawValue: Expr
 	}
 }
 
+extension Optional: ExpressibleByBooleanLiteral where Wrapped: ExpressibleByBooleanLiteral {
+	public typealias BooleanLiteralType = Wrapped.BooleanLiteralType
+
+	public init(booleanLiteral value: BooleanLiteralType) {
+		self = .some(Wrapped(booleanLiteral: value))
+	}
+}
+
 extension TransformedAttribute: ExpressibleByIntegerLiteral where RawValue: ExpressibleByIntegerLiteral, Transformer == IdentityTransformer<RawValue> {
 	public typealias IntegerLiteralType = RawValue.IntegerLiteralType
 
@@ -55,6 +71,14 @@ extension TransformedAttribute: ExpressibleByIntegerLiteral where RawValue: Expr
 	}
 }
 
+extension Optional: ExpressibleByIntegerLiteral where Wrapped: ExpressibleByIntegerLiteral {
+	public typealias IntegerLiteralType = Wrapped.IntegerLiteralType
+
+	public init(integerLiteral value: IntegerLiteralType) {
+		self = .some(Wrapped(integerLiteral: value))
+	}
+}
+
 // regretably, array and dictionary literals are not so easy because Dictionaries and Arrays
 // cannot be turned back into variadic arguments to pass onto the RawValue type's constructor.
 
@@ -79,6 +103,16 @@ extension TransformedAttribute: ExpressibleByDictionaryLiteral where RawValue: D
 	}
 }
 
+extension Optional: DictionaryType where Wrapped: DictionaryType {
+	public typealias Key = Wrapped.Key
+
+	public typealias Value = Wrapped.Value
+
+	public init<S>(_ keysAndValues: S, uniquingKeysWith combine: (Dictionary<Key, Value>.Value, Dictionary<Key, Value>.Value) throws -> Dictionary<Key, Value>.Value) rethrows where S : Sequence, S.Element == (Key, Value) {
+		self = try .some(Wrapped(keysAndValues, uniquingKeysWith: combine))
+	}
+}
+
 public protocol ArrayType {
 	associatedtype Element
 
@@ -94,3 +128,11 @@ extension TransformedAttribute: ExpressibleByArrayLiteral where RawValue: ArrayT
 		self.init(value: RawValue(elements))
 	}
 }
+
+extension Optional: ArrayType where Wrapped: ArrayType {
+	public typealias Element = Wrapped.Element
+
+	public init<S>(_ s: S) where Element == S.Element, S : Sequence {
+		self = .some(Wrapped(s))
+	}
+}

Sources/JSONAPITestLib/EntityCheck.swift

@@ -45,6 +45,10 @@ extension TransformedAttribute: AttributeTypeWithOptionalArray where RawValue: O
 private protocol OptionalRelationshipType {}
 extension Optional: OptionalRelationshipType where Wrapped: RelationshipType {}
 
+private protocol _RelationshipType {}
+extension ToOneRelationship: _RelationshipType {}
+extension ToManyRelationship: _RelationshipType {}
+
 public extension Entity {
 	public static func check(_ entity: Entity) throws {
 		var problems = [EntityCheckError]()
@@ -72,7 +76,8 @@ public extension Entity {
 		}
 
 		for relationship in relationshipsMirror.children {
-			if relationship.value as? RelationshipType == nil {
+			if relationship.value as? _RelationshipType == nil,
+				relationship.value as? OptionalRelationshipType == nil {
 				problems.append(.nonRelationship(named: relationship.label ?? "unnamed"))
 			}
 		}

Sources/JSONAPITestLib/Relationship+Literal.swift

@@ -7,38 +7,38 @@
 
 import JSONAPI
 
-extension ToOneRelationship: ExpressibleByNilLiteral where Relatable.WrappedIdentifier: ExpressibleByNilLiteral {
+extension ToOneRelationship: ExpressibleByNilLiteral where Identifiable.Identifier: ExpressibleByNilLiteral, MetaType == NoMetadata, LinksType == NoLinks {
 	public init(nilLiteral: ()) {
 
-		self.init(id: Relatable.WrappedIdentifier(nilLiteral: ()))
+		self.init(id: Identifiable.Identifier(nilLiteral: ()))
 	}
 }
 
-extension ToOneRelationship: ExpressibleByUnicodeScalarLiteral where Relatable.WrappedIdentifier: ExpressibleByUnicodeScalarLiteral {
-	public typealias UnicodeScalarLiteralType =  Relatable.WrappedIdentifier.UnicodeScalarLiteralType
+extension ToOneRelationship: ExpressibleByUnicodeScalarLiteral where Identifiable.Identifier: ExpressibleByUnicodeScalarLiteral, MetaType == NoMetadata, LinksType == NoLinks {
+	public typealias UnicodeScalarLiteralType =  Identifiable.Identifier.UnicodeScalarLiteralType
 
 	public init(unicodeScalarLiteral value: UnicodeScalarLiteralType) {
-		self.init(id: Relatable.WrappedIdentifier(unicodeScalarLiteral: value))
+		self.init(id: Identifiable.Identifier(unicodeScalarLiteral: value))
 	}
 }
 
-extension ToOneRelationship: ExpressibleByExtendedGraphemeClusterLiteral where Relatable.WrappedIdentifier: ExpressibleByExtendedGraphemeClusterLiteral {
-	public typealias ExtendedGraphemeClusterLiteralType =  Relatable.WrappedIdentifier.ExtendedGraphemeClusterLiteralType
+extension ToOneRelationship: ExpressibleByExtendedGraphemeClusterLiteral where Identifiable.Identifier: ExpressibleByExtendedGraphemeClusterLiteral, MetaType == NoMetadata, LinksType == NoLinks {
+	public typealias ExtendedGraphemeClusterLiteralType =  Identifiable.Identifier.ExtendedGraphemeClusterLiteralType
 
 	public init(extendedGraphemeClusterLiteral value: ExtendedGraphemeClusterLiteralType) {
-		self.init(id: Relatable.WrappedIdentifier(extendedGraphemeClusterLiteral: value))
+		self.init(id: Identifiable.Identifier(extendedGraphemeClusterLiteral: value))
 	}
 }
 
-extension ToOneRelationship: ExpressibleByStringLiteral where Relatable.WrappedIdentifier: ExpressibleByStringLiteral {
-	public typealias StringLiteralType = Relatable.WrappedIdentifier.StringLiteralType
+extension ToOneRelationship: ExpressibleByStringLiteral where Identifiable.Identifier: ExpressibleByStringLiteral, MetaType == NoMetadata, LinksType == NoLinks {
+	public typealias StringLiteralType = Identifiable.Identifier.StringLiteralType
 
 	public init(stringLiteral value: StringLiteralType) {
-		self.init(id: Relatable.WrappedIdentifier(stringLiteral: value))
+		self.init(id: Identifiable.Identifier(stringLiteral: value))
 	}
 }
 
-extension ToManyRelationship: ExpressibleByArrayLiteral {
+extension ToManyRelationship: ExpressibleByArrayLiteral where MetaType == NoMetadata, LinksType == NoLinks {
 	public typealias ArrayLiteralElement = Relatable.Identifier
 
 	public init(arrayLiteral elements: ArrayLiteralElement...) {

Tests/JSONAPITests/APIDescription/APIDescriptionTests.swift

@@ -10,6 +10,10 @@ import JSONAPI
 
 class APIDescriptionTests: XCTestCase {
 
+	func test_NoDescriptionString() {
+		XCTAssertEqual(String(describing: NoAPIDescription()), "No JSON:API Object")
+	}
+
 	func test_empty() {
 		let description = decoded(type: APIDescription<NoMetadata>.self, data: api_description_empty)
 

Tests/JSONAPITests/Attribute/Attribute+FunctorTests.swift

@@ -11,7 +11,7 @@ import JSONAPITestLib
 
 class Attribute_FunctorTests: XCTestCase {
 	func test_mapGuaranteed() {
-		let entity = try? TestType(attributes: .init(name: "Frankie", number: .init(rawValue: 22.0)))
+		let entity = try? TestType(attributes: .init(name: "Frankie", number: .init(rawValue: 22.0)), relationships: .none, meta: .none, links: .none)
 
 		XCTAssertNotNil(entity)
 
@@ -19,7 +19,7 @@ class Attribute_FunctorTests: XCTestCase {
 	}
 
 	func test_mapOptionalSuccess() {
-		let entity = try? TestType(attributes: .init(name: "Frankie", number: .init(rawValue: 22.0)))
+		let entity = try? TestType(attributes: .init(name: "Frankie", number: .init(rawValue: 22.0)), relationships: .none, meta: .none, links: .none)
 
 		XCTAssertNotNil(entity)
 
@@ -27,7 +27,7 @@ class Attribute_FunctorTests: XCTestCase {
 	}
 
 	func test_mapOptionalFailure() {
-		let entity = try? TestType(attributes: .init(name: "Frankie", number: .init(rawValue: 22.5)))
+		let entity = try? TestType(attributes: .init(name: "Frankie", number: .init(rawValue: 22.5)), relationships: .none, meta: .none, links: .none)
 
 		XCTAssertNotNil(entity)