Merge pull request #39 from mattpolzin/feature/add-poly-11

Add Include11 Type

JSONAPI.playground/Pages/Full Client & Server Example.xcplaygroundpage/Contents.swift

@@ -37,7 +37,7 @@ typealias ToManyRelationship<Entity: Relatable> = JSONAPI.ToManyRelationship<Ent
 // JSON:API Documents for this particular API to have Metadata, Links,
 // useful Errors, or an APIDescription (The *SPEC* calls this
 // "API Description" the "JSON:API Object").
-typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
+typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 
 // MARK: Entity Definitions
 

JSONAPI.playground/Pages/Sparse Fieldsets Example.xcplaygroundpage/Contents.swift

@@ -35,7 +35,7 @@ typealias ThingWithProperties = JSONAPI.ResourceObject<ThingWithPropertiesDescri
 //
 // NOTE: Using `JSONAPI.EncodableResourceBody` which means the document type will be `Encodable` but not `Decodable`.
 //
-typealias Document<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
+typealias Document<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 
 //
 // NOTE: Using `JSONAPI.EncodablePrimaryResource` which means the `ResourceBody` will be `Encodable` but not `Decodable.

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

@@ -24,7 +24,7 @@ let dogOwner: Person.Identifier? = dogFromData.flatMap { $0 ~> \.owner }
 
 
 // MARK: - 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>
+typealias AltSingleDogDocument = JSONAPI.Document<SingleResourceBody<AlternativeDog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, BasicJSONAPIError<String>>
 let altDogResponse = try! JSONDecoder().decode(AltSingleDogDocument.self, from: singleDogData)
 let altDogFromData = altDogResponse.body.primaryResource?.value
 let altDogHuman: Person.Identifier? = altDogFromData.flatMap { $0 ~> \.human }
@@ -55,19 +55,15 @@ print("-----")
 
 // MARK: - Pass successfully parsed body to other parts of the code
 
-/*
- ---- CRASHING IN XCODE 10.2 PLAYGROUND ----
-
 if case let .data(bodyData) = peopleResponse.body {
-	print("first person's name: \(bodyData.primary.values[0][\.fullName])")
+	print("first person's name: \(bodyData.primary.values[0].fullName)")
 } else {
 	print("no body data")
 }
- */
 
 
 // MARK: - Work in the abstract
-
+print("-----")
 func process<T: JSONAPIDocument>(document: T) {
 	guard case let .data(body) = document.body else {
 		return
@@ -75,3 +71,29 @@ func process<T: JSONAPIDocument>(document: T) {
 	let x: T.Body.Data = body
 }
 process(document: peopleResponse)
+
+// MARK: - Work with errors
+typealias ErrorDoc = JSONAPI.Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, BasicJSONAPIError<String>>
+
+let mockErrorData =
+"""
+{
+    "errors": [
+        {
+            "status": "500",
+            "title": "Internal Server Error",
+            "detail": "Server fell over while parsing your request."
+        }
+    ]
+}
+""".data(using: .utf8)!
+
+let errorResponse = try! JSONDecoder().decode(ErrorDoc.self, from: mockErrorData)
+
+switch errorResponse.body {
+case .data:
+    print("cool, data!")
+case .errors(let errors, let meta, let links):
+    let errorDetails = errors.compactMap { $0.payload?.detail }
+    print("error details: \(errorDetails)")
+}

JSONAPI.playground/Sources/Entities.swift

@@ -15,11 +15,11 @@ Please enjoy these examples, but allow me the forced casting and the lack of err
 ********/
 
 // MARK: - String as CreatableRawIdType
-var GlobalStringId: Int = 0
+var globalStringId: Int = 0
 extension String: CreatableRawIdType {
 	public static func unique() -> String {
-		GlobalStringId += 1
-		return String(GlobalStringId)
+		globalStringId += 1
+		return String(globalStringId)
 	}
 }
 
@@ -139,6 +139,6 @@ public enum HouseDescription: ResourceObjectDescription {
 
 public typealias House = ExampleEntity<HouseDescription>
 
-public typealias SingleDogDocument = JSONAPI.Document<SingleResourceBody<Dog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>
+public typealias SingleDogDocument = JSONAPI.Document<SingleResourceBody<Dog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, BasicJSONAPIError<String>>
 
-public typealias BatchPeopleDocument = JSONAPI.Document<ManyResourceBody<Person>, NoMetadata, NoLinks, Include2<Dog, House>, NoAPIDescription, UnknownJSONAPIError>
+public typealias BatchPeopleDocument = JSONAPI.Document<ManyResourceBody<Person>, NoMetadata, NoLinks, Include2<Dog, House>, NoAPIDescription, BasicJSONAPIError<String>>

JSONAPI.podspec

@@ -15,8 +15,8 @@ Pod::Spec.new do |spec|
   #  summary should be tweet-length, and the description more in depth.
   #
 
-  spec.name         = "JSONAPI"
-  spec.version      = "1.0.0"
+  spec.name         = "MP-JSONAPI"
+  spec.version      = "2.3.0"
   spec.summary      = "Swift Codable JSON API framework."
 
   # This description is used to generate tags and improve search results.
@@ -131,10 +131,11 @@ See the JSON API Spec here: https://jsonapi.org/format/
   #  where they will only apply to your library. If you depend on other Podspecs
   #  you can include multiple dependencies to ensure it works.
 
-  spec.swift_version = "5.0"
+  spec.swift_version = "5.1"
+  spec.module_name   = "JSONAPI"
   # spec.requires_arc = true
 
   # spec.xcconfig = { "HEADER_SEARCH_PATHS" => "$(SDKROOT)/usr/include/libxml2" }
-  spec.dependency "Poly", "~> 2.0"
+  spec.dependency "Poly", "~> 2.2"
 
 end

Package.resolved

@@ -6,8 +6,8 @@
         "repositoryURL": "https://github.com/mattpolzin/Poly.git",
         "state": {
           "branch": null,
-          "revision": "38051821d7ef49e590e26e819a2fe447e50be9ff",
-          "version": "2.0.1"
+          "revision": "b24fd3b41bf3126d4c6dede3708135182172af60",
+          "version": "2.2.0"
         }
       }
     ]

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.0
+// swift-tools-version:5.1
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
@@ -6,27 +6,27 @@ import PackageDescription
 let package = Package(
     name: "JSONAPI",
     platforms: [
-      .macOS(.v10_10),
-      .iOS(.v10)
+        .macOS(.v10_10),
+        .iOS(.v10)
     ],
     products: [
         .library(
             name: "JSONAPI",
             targets: ["JSONAPI"]),
-		.library(
-			name: "JSONAPITesting",
-			targets: ["JSONAPITesting"])
+        .library(
+            name: "JSONAPITesting",
+            targets: ["JSONAPITesting"])
     ],
     dependencies: [
-		.package(url: "https://github.com/mattpolzin/Poly.git", .upToNextMajor(from: "2.0.0")),
+        .package(url: "https://github.com/mattpolzin/Poly.git", .upToNextMajor(from: "2.2.0")),
     ],
     targets: [
         .target(
             name: "JSONAPI",
             dependencies: ["Poly"]),
-		.target(
-			name: "JSONAPITesting",
-			dependencies: ["JSONAPI"]),
+        .target(
+            name: "JSONAPITesting",
+            dependencies: ["JSONAPI"]),
         .testTarget(
             name: "JSONAPITests",
             dependencies: ["JSONAPI", "JSONAPITesting"]),
@@ -34,5 +34,5 @@ let package = Package(
             name: "JSONAPITestingTests",
             dependencies: ["JSONAPI", "JSONAPITesting"])
     ],
-  	swiftLanguageVersions: [.v5]
+    swiftLanguageVersions: [.v5]
 )

README.md

@@ -1,21 +1,37 @@
 # JSONAPI
-[![MIT license](http://img.shields.io/badge/license-MIT-lightgrey.svg)](http://opensource.org/licenses/MIT) [![Swift 5.0](http://img.shields.io/badge/Swift-5.0-blue.svg)](https://swift.org) [![Build Status](https://app.bitrise.io/app/c8295b9589aa401e/status.svg?token=vzcyqWD5bQ4xqQfZsaVzNw&branch=master)](https://app.bitrise.io/app/c8295b9589aa401e)
+[![MIT license](http://img.shields.io/badge/license-MIT-lightgrey.svg)](http://opensource.org/licenses/MIT) [![Swift 5.1](http://img.shields.io/badge/Swift-5.1-blue.svg)](https://swift.org) [![Build Status](https://app.bitrise.io/app/c8295b9589aa401e/status.svg?token=vzcyqWD5bQ4xqQfZsaVzNw&branch=master)](https://app.bitrise.io/app/c8295b9589aa401e)
 
 A Swift package for encoding to- and decoding from **JSON API** compliant requests and responses.
 
 See the JSON API Spec here: https://jsonapi.org/format/
 
-:warning: This library provides well-tested type safety when working with JSON:API 1.0, however the Swift compiler can sometimes have difficulty tracking down small typos when initializing `ResourceObjects`. Once the code is written correctly, it will compile, but tracking down the source of programmer errors can be an annoyance. This is mostly a concern when creating resource objects in-code (servers and test cases must do this). Writing a client that uses this framework to ingest JSON API Compliant API responses is much less painful. :warning:
+:warning: This library provides well-tested type safety when working with JSON:API 1.0. However, the Swift compiler can sometimes have difficulty tracking down small typos when initializing `ResourceObjects`. Once the code is written correctly, it will compile, but tracking down the source of programmer errors can be an annoyance. This is mostly a concern when creating resource objects in-code (servers and test cases must do this). Writing a client that uses this framework to ingest JSON API Compliant API responses is much less painful.
+
+## Quick Start
+
+:warning: The following Google Colab examples have correct code, but there appears to be an bug in the branch of the Swift compiler currently being used by the Google Colab Swift notebooks such that the `JSONAPI` package cannot be pulled in and you cannot run the examples in-browser.
+
+### Clientside
+- [Basic Example](https://colab.research.google.com/drive/1IS7lRSBGoiW02Vd1nN_rfdDbZvTDj6Te)
+- [Compound Example](https://colab.research.google.com/drive/1BdF0Kc7l2ixDfBZEL16FY6palweDszQU)
+- [Metadata Example](https://colab.research.google.com/drive/10dEESwiE9I3YoyfzVeOVwOKUTEgLT3qr)
+- [Custom Errors Example](https://colab.research.google.com/drive/1TIv6STzlHrkTf_-9Eu8sv8NoaxhZcFZH)
+
+### Serverside
+- [GET Example](https://colab.research.google.com/drive/1krbhzSfz8mwkBTQQnKUZJLEtYsJKSfYX)
+- [POST Example](https://colab.research.google.com/drive/1z3n70LwRY7vLIgbsMghvnfHA67QiuqpQ)
+
+### Combined
+This library works well when used by both the server responsible for serialization and the client responsible for deserialization. Check out the [example](#example) further down in this README.
 
 ## Table of Contents
-<!-- TOC depthFrom:1 depthTo:6 withLinks:1 updateOnSave:1 orderedList:0 -->
 
 - [JSONAPI](#jsonapi)
-	- [Table of Contents](#table-of-contents)
 	- [Primary Goals](#primary-goals)
 		- [Caveat](#caveat)
 	- [Dev Environment](#dev-environment)
 		- [Prerequisites](#prerequisites)
+		- [Swift Package Manager](#swift-package-manager)
 		- [CocoaPods](#cocoapods)
 		- [Xcode project](#xcode-project)
 		- [Running the Playground](#running-the-playground)
@@ -51,6 +67,9 @@ See the JSON API Spec here: https://jsonapi.org/format/
 			- [`IncludeType`](#includetype)
 			- [`APIDescriptionType`](#apidescriptiontype)
 			- [`Error`](#error)
+				- [`UnknownJSONAPIError`](#unknownjsonapierror)
+				- [`BasicJSONAPIError`](#basicjsonapierror)
+				- [`GenericJSONAPIError`](#genericjsonapierror)
 		- [`JSONAPI.Meta`](#jsonapimeta)
 		- [`JSONAPI.Links`](#jsonapilinks)
 		- [`JSONAPI.RawIdType`](#jsonapirawidtype)
@@ -69,8 +88,6 @@ See the JSON API Spec here: https://jsonapi.org/format/
 - [JSONAPI+Arbitrary](#jsonapiarbitrary)
 - [JSONAPI+OpenAPI](#jsonapiopenapi)
 
-<!-- /TOC -->
-
 ## Primary Goals
 
 The primary goals of this framework are:
@@ -86,20 +103,28 @@ If you find something wrong with this library and it isn't already mentioned und
 
 ## Dev Environment
 ### Prerequisites
-1. Swift 4.2+
+1. Swift 5.1+
 2. Swift Package Manager *OR* Cocoapods
 
+### Swift Package Manager
+Just include the following in your package's dependencies and add `JSONAPI` to the dependencies for any of your targets.
+```
+	.package(url: "https://github.com/mattpolzin/JSONAPI.git", .upToNextMajor(from: "2.2.0"))
+```
+
 ### CocoaPods
-To use this framework in your project via Cocoapods instead of Swift Package Manager, add the following dependencies to your Podfile.
+To use this framework in your project via Cocoapods, add the following dependencies to your Podfile.
 ```
 	pod 'Poly', :git => 'https://github.com/mattpolzin/Poly.git'
-	pod 'JSONAPI', :git => 'https://github.com/mattpolzin/JSONAPI.git'
+	pod 'MP-JSONAPI', :git => 'https://github.com/mattpolzin/JSONAPI.git'
 ```
 
 ### Xcode project
 To create an Xcode project for JSONAPI, run
 `swift package generate-xcodeproj`
 
+With Xcode 11+ you can also just open the folder containing your clone of this repository and begin working.
+
 ### Running the Playground
 To run the included Playground files, create an Xcode project using Swift Package Manager, then create an Xcode Workspace in the root of the repository and add both the generated Xcode project and the playground to the Workspace.
 
@@ -298,11 +323,18 @@ A resource object that does not have attributes can be described by adding the f
 typealias Attributes = NoAttributes
 ```
 
-`Attributes` can be accessed via the `subscript` operator of the `ResourceObject` type as follows:
+As of Swift 5.1, `Attributes` can be accessed via dynamic member keypath lookup as follows:
+```swift
+let favoriteColor: String = person.favoriteColor
+```
+
+🗒 `Attributes` can also be accessed via the older `subscript` operator as follows:
 ```swift
 let favoriteColor: String = person[\.favoriteColor]
 ```
 
+In both cases you retain type-safety. It is best practice to pick an attribute access syntax and stick with it. At some point in the future the syntax deemed less desirable may be deprecated.
+
 #### `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`.
@@ -341,7 +373,7 @@ You can also creator `Validators` and `ValidatedAttribute`s. A `Validator` is ju
 
 #### Computed `Attribute`
 
-You can add computed properties to your `ResourceObjectDescription.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.
+You can add computed properties to your `ResourceObjectDescription.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.
 
 ```swift
 public var fullName: Attribute<String> {
@@ -349,7 +381,7 @@ 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.
+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/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`:
@@ -374,7 +406,7 @@ The entirety of a JSON API request or response is encoded or decoded from- or to
 ```swift
 let decoder = JSONDecoder()
 
-let responseStructure = JSONAPI.Document<SingleResourceBody<Person>, NoMetadata, NoLinks, NoIncludes, UnknownJSONAPIError>.self
+let responseStructure = JSONAPI.Document<SingleResourceBody<Person>, NoMetadata, NoLinks, NoIncludes, BasicJSONAPIError<String>>.self
 
 let document = try decoder.decode(responseStructure, from: data)
 ```
@@ -423,7 +455,7 @@ The third generic type of a `JSONAPIDocument` is a `Links` struct. `Links` are d
 
 #### `IncludeType`
 
-The fourth generic type of a `JSONAPIDocument` is an `Include`. This type controls which types of `ResourceObject` are looked for when decoding the "included" part of the JSON API document. If you do not expect any included resource objects to be in the document, `NoIncludes` is the way to go. The `JSONAPI` framework provides `Include`s for up to six types of included resource objects. These are named `Include1`, `Include2`, `Include3`, and so on.
+The fourth generic type of a `JSONAPIDocument` is an `Include`. This type controls which types of `ResourceObject` are looked for when decoding the "included" part of the JSON API document. If you do not expect any included resource objects to be in the document, `NoIncludes` is the way to go. The `JSONAPI` framework provides `Include`s for up to 10 types of included resource objects. These are named `Include1`, `Include2`, `Include3`, and so on.
 
 **IMPORTANT**: The number trailing "Include" in these type names does not indicate a number of included resource objects, it indicates a number of _types_ of included resource objects. `Include1` can be used to decode any number of included resource objects as long as all the resource objects are of the same _type_.
 
@@ -441,7 +473,45 @@ You can supply any `JSONAPI.Meta` type as the metadata type of the API descripti
 
 #### `Error`
 
-The final generic type of a `JSONAPIDocument` is the `Error`. You should create an error type that can decode all the errors you expect your `JSONAPIDocument` to be able to decode. As prescribed by the **SPEC**, these errors will be found in the root document member `errors`.
+The final generic type of a `JSONAPIDocument` is the `Error`.
+
+You can either create an error type that can handle all the errors you expect your `JSONAPIDocument` to be able to encode/decode or use an out-of-box error type described here. As prescribed by the **SPEC**, these errors will be found under the root document key `errors`.
+
+##### `UnknownJSONAPIError`
+The `UnknownJSONAPIError` type will always succeed in parsing errors but it will not give you any information about what error occurred. You will generally get more bang for your buck out of the next error type described.
+
+##### `BasicJSONAPIError`
+The `BasicJSONAPIError` type will always succeed unless it is faced with an `id` field of an unexpected type, although it still "succeeds" in falling back to its `.unknown` case when that happens. This type extracts _most_ of the fields the **SPEC** describes [here](https://jsonapi.org/format/#error-objects). Because all of these fields are optional in the **SPEC**, they are optional on the `BasicJSONAPIError` type. You will have to create your own error type if you want to define certain fields as non-optional or parse metadata or links out of error objects.
+
+🗒Metadata and links are supported at the Document level for error responses, the are just not supported hanging off of the individual errors in the `errors` array of the response when using this error type.
+
+The `BasicJSONAPIError` type is generic on one thing: The type it expects for the `id` field. If you expect integer `ids` back, you use `BasicJSONAPIError<Int>`. The same can be done for `String` or any other type that is both `Codable` and `Equatable`. You can even employ something like `AnyCodable` from *Flight-School* as your id field type. If you only need to handle a small subset of possible `id` field types, you can also use the `Poly` library that is already a dependency of `JSONAPI`. For example, you might expect a mix of `String` and `Int` ids for some reason: `BasicJSONAPIError<Either<Int, String>>`.
+
+The two easiest ways to access the available properties of an error response are under the `payload` property of the error (this property is `nil` if the error was parsed as `.unknown`) or by asking the error for its `definedFields` dictionary.
+
+As an example, let's say you have the following `Document` type that is destined for errors:
+```swift
+typealias ErrorDoc = JSONAPI.Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, BasicJSONAPIError<String>>
+```
+And you've parsed an error response
+```swift
+let errorResponse = try! JSONDecoder().decode(ErrorDoc.self, from: mockErrorData)
+```
+You can get at the `Document` body and errors in a couple of different ways, but for one you can switch on the body:
+```swift
+switch errorResponse.body {
+case .data:
+    print("cool, data!")
+
+case .errors(let errors, let meta, let links):
+    let errorDetails = errors.compactMap { $0.payload?.detail }
+
+    print("error details: \(errorDetails)")
+}
+```
+
+##### `GenericJSONAPIError`
+This type makes it simple to use your own error payload structures as `JSONAPIError` types. Simply define a `Codable` and `Equatable` struct and then use `GenericJSONAPIError<YourType>` as the error type for a `Document`.
 
 ### `JSONAPI.Meta`
 
@@ -491,12 +561,12 @@ There is a sparse fieldsets example included with this repository as a Playgroun
 #### Sparse Fieldset `typealias` comparisons
 You might have found a `typealias` like the following for encoding/decoding `JSONAPI.Document`s (note the primary resource body is a `JSONAPI.ResourceBody`):
 ```swift
-typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
+typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 ```
 
 In order to support sparse fieldsets (which are encode-only), the following companion `typealias` would be useful (note the primary resource body is a `JSONAPI.EncodableResourceBody`):
 ```swift
-typealias SparseDocument<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
+typealias SparseDocument<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 ```
 
 ### Custom Attribute or Relationship Key Mapping
@@ -611,7 +681,7 @@ typealias User = JSONAPI.ResourceObject<UserDescription, NoMetadata, NoLinks, St
 Given a value `user` of the above resource object type, you can access the `createdAt` attribute just like you would any other:
 
 ```swift
-let createdAt = user[\.createdAt]
+let createdAt = user.createdAt
 ```
 
 This works because `createdAt` is defined in the form: `var {name}: ({ResourceObject}) -> {Value}` where `{ResourceObject}` is the `JSONAPI.ResourceObject` described by the `ResourceObjectDescription` containing the meta-attribute.
@@ -632,7 +702,7 @@ enum UserDescription: ResourceObjectDescription {
 	struct Relationships: JSONAPI.Relationships {
 		public var friend: (User) -> User.Identifier {
 			return { user in
-				return User.Identifier(rawValue: user[\.friend_id])
+				return User.Identifier(rawValue: user.friend_id)
 			}
 		}
 	}
@@ -684,7 +754,7 @@ typealias ToManyRelationship<Entity: Relatable> = JSONAPI.ToManyRelationship<Ent
 // JSON:API Documents for this particular API to have Metadata, Links,
 // useful Errors, or an APIDescription (The *SPEC* calls this
 // "API Description" the "JSON:API Object").
-typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, UnknownJSONAPIError>
+typealias Document<PrimaryResourceBody: JSONAPI.ResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 
 // MARK: Entity Definitions
 

Sources/JSONAPI/Document/Includes.swift

@@ -161,3 +161,19 @@ extension Includes where I: _Poly9 {
 		return values.compactMap { $0.i }
 	}
 }
+
+// MARK: - 10 includes
+public typealias Include10 = Poly10
+extension Includes where I: _Poly10 {
+    public subscript(_ lookup: I.J.Type) -> [I.J] {
+        return values.compactMap { $0.j }
+    }
+}
+
+// MARK: - 11 includes
+public typealias Include11 = Poly11
+extension Includes where I: _Poly11 {
+    public subscript(_ lookup: I.K.Type) -> [I.K] {
+        return values.compactMap { $0.k }
+    }
+}

Sources/JSONAPI/Error/BasicJSONAPIError.swift

@@ -0,0 +1,96 @@
+//
+//  BasicJSONAPIError.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 9/29/19.
+//
+
+/// Most of the JSON:API Spec defined Error fields.
+public struct BasicJSONAPIErrorPayload<IdType: Codable & Equatable>: Codable, Equatable, ErrorDictType {
+    /// a unique identifier for this particular occurrence of the problem
+    public let id: IdType?
+//    public let links: Links? // we skip this for now to avoid adding complexity to using this basic type.
+    /// the HTTP status code applicable to this problem
+    public let status: String?
+    /// an application-specific error code
+    public let code: String?
+    /// a short, human-readable summary of the problem that SHOULD NOT change from occurrence to occurrence of the problem, except for purposes of localization
+    public let title: String?
+    /// a human-readable explanation specific to this occurrence of the problem. Like `title`, this field’s value can be localized
+    public let detail: String?
+    /// an object containing references to the source of the error
+    public let source: Source?
+//    public let meta: Meta? // we skip this for now to avoid adding complexity to using this basic type
+
+    public init(id: IdType? = nil,
+                status: String? = nil,
+                code: String? = nil,
+                title: String? = nil,
+                detail: String? = nil,
+                source: Source? = nil) {
+        self.id = id
+        self.status = status
+        self.code = code
+        self.title = title
+        self.detail = detail
+        self.source = source
+    }
+
+    public struct Source: Codable, Equatable {
+        /// a JSON Pointer [RFC6901] to the associated entity in the request document [e.g. "/data" for a primary data object, or "/data/attributes/title" for a specific attribute].
+        public let pointer: String?
+        /// which URI query parameter caused the error
+        public let parameter: String?
+
+        public init(pointer: String? = nil,
+                    parameter: String? = nil) {
+            self.pointer = pointer
+            self.parameter = parameter
+        }
+    }
+
+    public var definedFields: [String: String] {
+        let keysAndValues = [
+            id.map { ("id", String(describing: $0)) },
+            status.map { ("status", $0) },
+            code.map { ("code", $0) },
+            title.map { ("title", $0) },
+            detail.map { ("detail", $0) },
+            source.flatMap { $0.pointer.map { ("pointer", $0) } },
+            source.flatMap { $0.parameter.map { ("parameter", $0) } }
+            ].compactMap { $0 }
+        return Dictionary(uniqueKeysWithValues: keysAndValues)
+    }
+}
+
+/// `BasicJSONAPIError` optionally decodes many possible fields
+/// specified by the JSON:API 1.0 Spec. It gives no type-guarantees of what
+/// will be non-nil, but could provide good diagnostic information when
+/// you do not know what error structure to expect.
+///
+/// ```
+/// Fields:
+/// - id
+/// - status
+/// - code
+/// - title
+/// - detail
+/// - source
+///   - pointer
+///   - parameter
+/// ```
+///
+/// The JSON:API Spec does not dictate the type of this particular Id field,
+/// so you must specify whether to expect, for example, an `Int` or a `String`
+/// in the id field.
+///
+/// Something like `AnyCodable` from *Flight-School* could be
+/// a good option if you do not know what to expect. You could also use
+/// `Either<Int, String>` (provided by the `Poly` package that is
+/// already a dependency of `JSONAPI`).
+///
+///  - Important: The `definedFields` property will include fields
+///     with non-nil values in a flattened way. There will be no `source` key
+///     but there will be `pointer` and `parameter` keys (if those values
+///     are non-nil).
+public typealias BasicJSONAPIError<IdType: Codable & Equatable> = GenericJSONAPIError<BasicJSONAPIErrorPayload<IdType>>

Sources/JSONAPI/Error/GenericJSONAPIError.swift

@@ -0,0 +1,65 @@
+//
+//  GenericJSONAPIError.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 9/29/19.
+//
+
+/// `GenericJSONAPIError` can be used to specify whatever error
+/// payload you expect to need to parse in responses and handle any
+/// other payload structure as `.unknownError`.
+public enum GenericJSONAPIError<ErrorPayload: Codable & Equatable>: JSONAPIError {
+    case unknownError
+    case error(ErrorPayload)
+
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.singleValueContainer()
+
+        do {
+            self = .error(try container.decode(ErrorPayload.self))
+        } catch {
+            self = .unknown
+        }
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.singleValueContainer()
+        switch self {
+        case .error(let payload):
+            try container.encode(payload)
+        case .unknownError:
+            try container.encode("unknown")
+        }
+    }
+
+    public static var unknown: Self {
+        return .unknownError
+    }
+}
+
+public extension GenericJSONAPIError {
+    var payload: ErrorPayload? {
+        switch self {
+        case .unknownError:
+            return nil
+        case .error(let payload):
+            return payload
+        }
+    }
+}
+
+public protocol ErrorDictType {
+    var definedFields: [String: String] { get }
+}
+
+extension GenericJSONAPIError: ErrorDictType where ErrorPayload: ErrorDictType {
+    /// Get a dictionary of all defined fields and their values.
+    public var definedFields: [String: String] {
+        switch self {
+        case .unknownError:
+            return [:]
+        case .error(let basicPayload):
+            return basicPayload.definedFields
+        }
+    }
+}

Sources/JSONAPI/Error/JSONAPIError.swift

@@ -1,5 +1,5 @@
 //
-//  Error.swift
+//  JSONAPIError.swift
 //  JSONAPI
 //
 //  Created by Mathew Polzin on 11/10/18.
@@ -11,7 +11,10 @@ public protocol JSONAPIError: Swift.Error, Equatable, Codable {
 
 /// `UnknownJSONAPIError` can actually be used in any sitaution
 /// where you don't know what errors are possible _or_ you just don't
-/// care what errors might show up.
+/// care what errors might show up. If you don't know how the error
+/// will be structured but you would like to have access to more
+/// information the server might be providing in the error payload,
+/// use `BasicJSONAPIError` instead.
 public enum UnknownJSONAPIError: JSONAPIError {
 	case unknownError
 	
@@ -24,7 +27,7 @@ public enum UnknownJSONAPIError: JSONAPIError {
 		try container.encode("unknown")
 	}
 	
-	public static var unknown: UnknownJSONAPIError {
+	public static var unknown: Self {
 		return .unknownError
 	}
 }

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/Poly+PrimaryResource.swift

@@ -74,3 +74,13 @@ extension Poly8: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped,
 extension Poly9: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped, G: EncodablePolyWrapped, H: EncodablePolyWrapped, I: EncodablePolyWrapped {}
 
 extension Poly9: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped, I: PolyWrapped {}
+
+// MARK: - 10 types
+extension Poly10: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped, G: EncodablePolyWrapped, H: EncodablePolyWrapped, I: EncodablePolyWrapped, J: EncodablePolyWrapped {}
+
+extension Poly10: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped, I: PolyWrapped, J: PolyWrapped {}
+
+// MARK: - 11 types
+extension Poly11: EncodablePrimaryResource, OptionalEncodablePrimaryResource where A: EncodablePolyWrapped, B: EncodablePolyWrapped, C: EncodablePolyWrapped, D: EncodablePolyWrapped, E: EncodablePolyWrapped, F: EncodablePolyWrapped, G: EncodablePolyWrapped, H: EncodablePolyWrapped, I: EncodablePolyWrapped, J: EncodablePolyWrapped, K: EncodablePolyWrapped {}
+
+extension Poly11: PrimaryResource, OptionalPrimaryResource where A: PolyWrapped, B: PolyWrapped, C: PolyWrapped, D: PolyWrapped, E: PolyWrapped, F: PolyWrapped, G: PolyWrapped, H: PolyWrapped, I: PolyWrapped, J: PolyWrapped, K: PolyWrapped {}

Sources/JSONAPI/Resource/ResourceObject.swift

@@ -66,8 +66,9 @@ public protocol ResourceObjectProxyDescription: JSONTyped {
 public protocol ResourceObjectDescription: ResourceObjectProxyDescription where Attributes: JSONAPI.Attributes, Relationships: JSONAPI.Relationships {}
 
 /// ResourceObjectProxy is a protocol that can be used to create
-/// types that _act_ like Entities but cannot be encoded
-/// or decoded as Entities.
+/// types that _act_ like ResourceObject but cannot be encoded
+/// or decoded as ResourceObjects.
+@dynamicMemberLookup
 public protocol ResourceObjectProxy: Equatable, JSONTyped {
 	associatedtype Description: ResourceObjectProxyDescription
 	associatedtype EntityRawIdType: JSONAPI.MaybeRawId
@@ -91,7 +92,7 @@ public protocol ResourceObjectProxy: Equatable, JSONTyped {
 }
 
 extension ResourceObjectProxy {
-	/// The JSON API compliant "type" of this `Entity`.
+	/// The JSON API compliant "type" of this `ResourceObject`.
 	public static var jsonType: String { return Description.jsonType }
 }
 
@@ -151,7 +152,7 @@ extension ResourceObject: CustomStringConvertible {
 	}
 }
 
-// MARK: Convenience initializers
+// MARK: - Convenience initializers
 extension ResourceObject where EntityRawIdType: CreatableRawIdType {
 	public init(attributes: Description.Attributes, relationships: Description.Relationships, meta: MetaType, links: LinksType) {
 		self.id = ResourceObject.Id()
@@ -402,7 +403,7 @@ extension ResourceObject where MetaType == NoMetadata, LinksType == NoLinks, Ent
 }
 */
 
-// MARK: Pointer for Relationships use.
+// MARK: - Pointer for Relationships use
 public extension ResourceObject where EntityRawIdType: JSONAPI.RawIdType {
 
 	/// A `ResourceObject.Pointer` is a `ToOneRelationship` with no metadata or links.
@@ -428,7 +429,7 @@ public extension ResourceObject where EntityRawIdType: JSONAPI.RawIdType {
 	}
 }
 
-// MARK: Identifying Unidentified Entities
+// MARK: - Identifying Unidentified Entities
 public extension ResourceObject where EntityRawIdType == Unidentified {
 	/// Create a new `ResourceObject` from this one with a newly created
 	/// unique Id of the given type.
@@ -449,31 +450,55 @@ public extension ResourceObject where EntityRawIdType: CreatableRawIdType {
 	}
 }
 
-// MARK: Attribute Access
+// MARK: - Attribute Access
 public extension ResourceObjectProxy {
+    // MARK: Keypath Subscript Lookup
 	/// Access the attribute at the given keypath. This just
 	/// allows you to write `resourceObject[\.propertyName]` instead
-	/// of `resourceObject.attributes.propertyName`.
+	/// of `resourceObject.attributes.propertyName.value`.
 	subscript<T: AttributeType>(_ path: KeyPath<Description.Attributes, T>) -> T.ValueType {
 		return attributes[keyPath: path].value
 	}
 
 	/// Access the attribute at the given keypath. This just
 	/// allows you to write `resourceObject[\.propertyName]` instead
-	/// of `resourceObject.attributes.propertyName`.
+	/// of `resourceObject.attributes.propertyName.value`.
 	subscript<T: AttributeType>(_ path: KeyPath<Description.Attributes, T?>) -> T.ValueType? {
 		return attributes[keyPath: path]?.value
 	}
 
 	/// Access the attribute at the given keypath. This just
 	/// allows you to write `resourceObject[\.propertyName]` instead
-	/// of `resourceObject.attributes.propertyName`.
+	/// of `resourceObject.attributes.propertyName.value`.
 	subscript<T: AttributeType, U>(_ path: KeyPath<Description.Attributes, T?>) -> U? where T.ValueType == U? {
 		// Implementation Note: Handles Transform that returns optional
 		// type.
 		return attributes[keyPath: path].flatMap { $0.value }
 	}
 
+    // MARK: Dynaminc Member Keypath Lookup
+    /// Access the attribute at the given keypath. This just
+    /// allows you to write `resourceObject[\.propertyName]` instead
+    /// of `resourceObject.attributes.propertyName.value`.
+    subscript<T: AttributeType>(dynamicMember path: KeyPath<Description.Attributes, T>) -> T.ValueType {
+        return attributes[keyPath: path].value
+    }
+
+    /// Access the attribute at the given keypath. This just
+    /// allows you to write `resourceObject[\.propertyName]` instead
+    /// of `resourceObject.attributes.propertyName.value`.
+    subscript<T: AttributeType>(dynamicMember path: KeyPath<Description.Attributes, T?>) -> T.ValueType? {
+        return attributes[keyPath: path]?.value
+    }
+
+    /// Access the attribute at the given keypath. This just
+    /// allows you to write `resourceObject[\.propertyName]` instead
+    /// of `resourceObject.attributes.propertyName.value`.
+    subscript<T: AttributeType, U>(dynamicMember path: KeyPath<Description.Attributes, T?>) -> U? where T.ValueType == U? {
+        return attributes[keyPath: path].flatMap { $0.value }
+    }
+
+    // MARK: Direct Keypath Subscript Lookup
 	/// Access the storage of the attribute at the given keypath. This just
     /// allows you to write `resourceObject[direct: \.propertyName]` instead
 	/// of `resourceObject.attributes.propertyName`.
@@ -487,16 +512,24 @@ public extension ResourceObjectProxy {
 	}
 }
 
-// MARK: Meta-Attribute Access
+// MARK: - Meta-Attribute Access
 public extension ResourceObjectProxy {
+    // MARK: Keypath Subscript Lookup
 	/// Access an attribute requiring a transformation on the RawValue _and_
 	/// a secondary transformation on this entity (self).
 	subscript<T>(_ path: KeyPath<Description.Attributes, (Self) -> T>) -> T {
 		return attributes[keyPath: path](self)
 	}
+
+    // MARK: Dynamic Member Keypath Lookup
+    /// Access an attribute requiring a transformation on the RawValue _and_
+    /// a secondary transformation on this entity (self).
+    subscript<T>(dynamicMember path: KeyPath<Description.Attributes, (Self) -> T>) -> T {
+        return attributes[keyPath: path](self)
+    }
 }
 
-// MARK: Relationship Access
+// MARK: - Relationship Access
 public extension ResourceObjectProxy {
 	/// Access to an Id of a `ToOneRelationship`.
 	/// This allows you to write `resourceObject ~> \.other` instead
@@ -538,7 +571,7 @@ public extension ResourceObjectProxy {
 	}
 }
 
-// MARK: Meta-Relationship Access
+// MARK: - Meta-Relationship Access
 public extension ResourceObjectProxy {
 	/// Access to an Id of a `ToOneRelationship`.
 	/// This allows you to write `resourceObject ~> \.other` instead

Tests/JSONAPITests/Attribute/Attribute+FunctorTests.swift

@@ -16,6 +16,7 @@ class Attribute_FunctorTests: XCTestCase {
 		XCTAssertNotNil(entity)
 
 		XCTAssertEqual(entity?[\.computedString], "Frankie2")
+        XCTAssertEqual(entity?.computedString, "Frankie2")
 	}
 
 	func test_mapOptionalSuccess() {
@@ -24,6 +25,7 @@ class Attribute_FunctorTests: XCTestCase {
 		XCTAssertNotNil(entity)
 
 		XCTAssertEqual(entity?[\.computedNumber], 22)
+        XCTAssertEqual(entity?.computedNumber, 22)
 	}
 
 	func test_mapOptionalFailure() {
@@ -32,6 +34,7 @@ class Attribute_FunctorTests: XCTestCase {
 		XCTAssertNotNil(entity)
 
 		XCTAssertNil(entity?[\.computedNumber])
+        XCTAssertNil(entity?.computedNumber)
 	}
 }
 

Tests/JSONAPITests/Attribute/AttributeTests.swift

@@ -77,12 +77,37 @@ extension AttributeTests {
 		}
 	}
 
-	enum IntToString: Transformer {
+	enum IntToString: ReversibleTransformer {
 		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/Computed Properties/ComputedPropertiesTests.swift

@@ -15,6 +15,7 @@ class ComputedPropertiesTests: XCTestCase {
 
 		XCTAssertEqual(entity.id, "1234")
 		XCTAssertEqual(entity[\.name], "Sarah")
+        XCTAssertEqual(entity.name, "Sarah")
 		XCTAssertEqual(entity ~> \.other, "5678")
 		XCTAssertNoThrow(try TestType.check(entity))
 	}
@@ -27,6 +28,7 @@ class ComputedPropertiesTests: XCTestCase {
 		let entity = decoded(type: TestType.self, data: computed_property_attribute)
 
 		XCTAssertEqual(entity[\.computed], "Sarah2")
+        XCTAssertEqual(entity.computed, "Sarah2")
         XCTAssertEqual(entity[direct: \.directSecretsOut], "shhhh")
 	}
 

Tests/JSONAPITests/Custom Attributes Tests/CustomAttributesTests.swift

@@ -14,7 +14,9 @@ class CustomAttributesTests: XCTestCase {
 		let entity = decoded(type: CustomAttributeEntity.self, data: customAttributeEntityData)
 
 		XCTAssertEqual(entity[\.firstName], "Cool")
+        XCTAssertEqual(entity.firstName, "Cool")
 		XCTAssertEqual(entity[\.name], "Cool Name")
+        XCTAssertEqual(entity.name, "Cool Name")
 		XCTAssertNoThrow(try CustomAttributeEntity.check(entity))
 	}
 
@@ -27,7 +29,9 @@ class CustomAttributesTests: XCTestCase {
 		let entity = decoded(type: CustomKeysEntity.self, data: customAttributeEntityData)
 
 		XCTAssertEqual(entity[\.firstNameSilly], "Cool")
+        XCTAssertEqual(entity.firstNameSilly, "Cool")
 		XCTAssertEqual(entity[\.lastNameSilly], "Name")
+        XCTAssertEqual(entity.lastNameSilly, "Name")
 		XCTAssertNoThrow(try CustomKeysEntity.check(entity))
 	}
 

Tests/JSONAPITests/Error/BasicJSONAPIErrorTests.swift

@@ -0,0 +1,131 @@
+//
+//  BasicJSONAPIErrorTests.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 9/29/19.
+//
+
+import Foundation
+import JSONAPI
+import XCTest
+import Poly
+
+final class BasicJSONAPIErrorTests: XCTestCase {
+    func test_initAndEquality() {
+        let unknown1 = BasicJSONAPIError<String>.unknown
+        let unknown2 = BasicJSONAPIError<String>.unknownError
+        XCTAssertEqual(unknown1, unknown2)
+        let unknown3 = BasicJSONAPIError<Int>.unknownError
+        XCTAssertEqual(unknown3, .unknown)
+
+        let _ = BasicJSONAPIError<Int>.error(.init(id: nil,
+                                                   status: nil,
+                                                   code: nil,
+                                                   title: nil,
+                                                   detail: nil,
+                                                   source: nil))
+        let _ = BasicJSONAPIError<String>.error(.init(id: nil,
+                                                      status: nil,
+                                                      code: nil,
+                                                      title: nil,
+                                                      detail: nil,
+                                                      source: nil))
+
+        let intError = BasicJSONAPIError<Int>.error(.init(id: 2,
+                                                          status: nil,
+                                                          code: nil,
+                                                          title: nil,
+                                                          detail: nil,
+                                                          source: nil))
+        XCTAssertEqual(intError.payload?.id, 2)
+        XCTAssertNotEqual(intError, unknown3)
+
+        let stringError = BasicJSONAPIError<String>.error(.init(id: "hello",
+                                                                status: nil,
+                                                                code: nil,
+                                                                title: nil,
+                                                                detail: nil,
+                                                                source: nil))
+        XCTAssertEqual(stringError.payload?.id, "hello")
+        XCTAssertNotEqual(stringError, unknown1)
+
+        let wellPopulatedError = BasicJSONAPIError<Int>.error(.init(id: 10,
+                                                                    status: "404",
+                                                                    code: "12",
+                                                                    title: "Missing",
+                                                                    detail: "Resource was not found",
+                                                                    source: .init(pointer: "/data/attributes/id", parameter: "id")))
+        XCTAssertEqual(wellPopulatedError.payload?.id, 10)
+        XCTAssertEqual(wellPopulatedError.payload?.status, "404")
+        XCTAssertEqual(wellPopulatedError.payload?.code, "12")
+        XCTAssertEqual(wellPopulatedError.payload?.title, "Missing")
+        XCTAssertEqual(wellPopulatedError.payload?.detail, "Resource was not found")
+        XCTAssertEqual(wellPopulatedError.payload?.source?.pointer, "/data/attributes/id")
+        XCTAssertEqual(wellPopulatedError.payload?.source?.parameter, "id")
+
+        XCTAssertNotEqual(wellPopulatedError, intError)
+    }
+
+    func test_definedFields() {
+        let unpopulatedError = BasicJSONAPIError<Int>.error(.init(id: nil,
+                                                                  status: nil,
+                                                                  code: nil,
+                                                                  title: nil,
+                                                                  detail: nil,
+                                                                  source: nil))
+        XCTAssertEqual(unpopulatedError.definedFields.count, 0)
+
+        let wellPopulatedError = BasicJSONAPIError<Int>.error(.init(id: 10,
+                                                                    status: "404",
+                                                                    code: "12",
+                                                                    title: "Missing",
+                                                                    detail: "Resource was not found",
+                                                                    source: .init(pointer: "/data/attributes/id", parameter: "id")))
+        XCTAssertEqual(wellPopulatedError.definedFields.count, 7)
+        XCTAssertEqual(wellPopulatedError.definedFields["id"], "10")
+        XCTAssertEqual(wellPopulatedError.definedFields["status"], "404")
+        XCTAssertEqual(wellPopulatedError.definedFields["code"], "12")
+        XCTAssertEqual(wellPopulatedError.definedFields["title"], "Missing")
+        XCTAssertEqual(wellPopulatedError.definedFields["detail"], "Resource was not found")
+        XCTAssertEqual(wellPopulatedError.definedFields["pointer"], "/data/attributes/id")
+        XCTAssertEqual(wellPopulatedError.definedFields["parameter"], "id")
+    }
+
+    func test_decodeAFewExamples() {
+        let datas = [
+"""
+{
+    "id": "hello"
+}
+""",
+"""
+{
+    "id": 1234
+}
+""",
+"""
+{
+    "status": "404",
+    "title": "Missing",
+    "links": {
+        "about": "https://google.com"
+    }
+}
+""",
+"""
+{
+    "status": 404
+}
+"""
+        ].map { $0.data(using: .utf8)! }
+
+        let errors = datas
+            .map { decoded(type: BasicJSONAPIError<Either<Int, String>>.self, data: $0) }
+
+        XCTAssertEqual(errors[0].payload?.id, .init("hello"))
+        XCTAssertEqual(errors[1].payload?.id, .init(1234))
+        XCTAssertEqual(errors[2].payload?.status, "404")
+        XCTAssertEqual(errors[2].payload?.title, "Missing")
+        XCTAssertEqual(errors[3], .unknown)
+    }
+}