Fix return type of success document after adding includes

Resource Object replacing and tapping

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

@@ -0,0 +1,124 @@
+//: [Previous](@previous)
+
+import Foundation
+import JSONAPI
+
+/*******
+
+ Please enjoy these examples, but allow me the forced casting and the lack of error checking for the sake of brevity.
+
+ This playground focuses on receiving a resource, making some changes, and then creating a request body for a PATCH request.
+ As with all examples in these playround pages, no actual networking code will be provided.
+
+ ********/
+
+// Mock up a server response
+let mockDogData = """
+{
+    "data": {
+        "id": "1234",
+        "type": "dogs",
+        "attributes": {
+            "name": "Sparky"
+        },
+        "relationships": {
+            "owner": {
+                "data": null
+            }
+        }
+    }
+}
+""".data(using: .utf8)!
+
+//
+// MARK: - EXAMPLE 1 (Mutable Attributes)
+//
+
+// pretend to have requested a Dog and received the mock data
+// now parse it.
+let parsedResponse = try! JSONDecoder().decode(MutableDogDocument.self, from: mockDogData)
+
+// extract our Dog (skipping over any robustness to handle errors)
+var dog = parsedResponse.body.primaryResource!.value
+print("Received dog named: \(dog.name)")
+
+// change the dog's name
+let changedDog = dog.tappingAttributes { $0.name = .init(value: "Julia") }
+
+// create a document to be used as a request body for a PATCH request
+let patchRequest = MutableDogDocument(apiDescription: .none,
+                                      body: .init(resourceObject: changedDog),
+                                      includes: .none,
+                                      meta: .none,
+                                      links: .none)
+
+// encode and send off to server
+let encodedPatchRequest = try! JSONEncoder().encode(patchRequest)
+print("----")
+print(String(data: encodedPatchRequest, encoding:.utf8)!)
+
+
+//
+// MARK: - EXAMPLE 2 (Immutable Attributes)
+//
+print()
+print("####")
+print()
+
+// pretend to have requested a Dog and received the mock data
+// now parse it.
+let parsedResponse2 = try! JSONDecoder().decode(SingleDogDocument.self, from: mockDogData)
+
+// extract our Dog (skipping over any robustness to handle errors)
+var dog2 = parsedResponse2.body.primaryResource!.value
+print("Received dog named: \(dog2.name)")
+
+// change the dog's name
+let changedDog2 = dog2.replacingAttributes { _ in
+    return .init(name: .init(value: "Nigel"))
+}
+
+// create a document to be used as a request body for a PATCH request
+let patchRequest2 = SingleDogDocument(apiDescription: .none,
+                                      body: .init(resourceObject: changedDog2),
+                                      includes: .none,
+                                      meta: .none,
+                                      links: .none)
+
+// encode and send off to server
+let encodedPatchRequest2 = try! JSONEncoder().encode(patchRequest2)
+print("----")
+print(String(data: encodedPatchRequest2, encoding:.utf8)!)
+
+
+//
+// MARK: - EXAMPLE 3 (Change relationship)
+//
+print()
+print("####")
+print()
+
+// pretend to have requested a Dog and received the mock data
+// now parse it.
+let parsedResponse3 = try! JSONDecoder().decode(SingleDogDocument.self, from: mockDogData)
+
+// extract our Dog (skipping over any robustness to handle errors)
+var dog3 = parsedResponse2.body.primaryResource!.value
+print("Received dog with owner: \(dog3 ~> \.owner)")
+
+// give the dog an owner
+let changedDog3 = dog3.replacingRelationships { _ in
+    return .init(owner: .init(id: Id(rawValue: "1")))
+}
+
+// create a document to be used as a request body for a PATCH request
+let patchRequest3 = SingleDogDocument(apiDescription: .none,
+                                      body: .init(resourceObject: changedDog3),
+                                      includes: .none,
+                                      meta: .none,
+                                      links: .none)
+
+// encode and send off to server
+let encodedPatchRequest3 = try! JSONEncoder().encode(patchRequest3)
+print("----")
+print(String(data: encodedPatchRequest3, encoding:.utf8)!)

JSONAPI.playground/Sources/Entities.swift

@@ -119,6 +119,29 @@ public enum AlternativeDogDescription: ResourceObjectDescription {
 
 public typealias AlternativeDog = ExampleEntity<AlternativeDogDescription>
 
+public enum MutableDogDescription: ResourceObjectDescription {
+
+    public static var jsonType: String { return "dogs" }
+
+    public struct Attributes: JSONAPI.Attributes {
+        public var name: Attribute<String>
+
+        public init(name: Attribute<String>) {
+            self.name = name
+        }
+    }
+
+    public struct Relationships: JSONAPI.Relationships {
+        public var owner: ToOne<Person?>
+
+        public init(owner: ToOne<Person?>) {
+            self.owner = owner
+        }
+    }
+}
+
+public typealias MutableDog = ExampleEntity<MutableDogDescription>
+
 public extension ResourceObject where Description == DogDescription, MetaType == NoMetadata, LinksType == NoLinks, EntityRawIdType == String {
 	init(name: String, owner: Person?) throws {
 		self = Dog(attributes: .init(name: .init(value: name)), relationships: DogDescription.Relationships(owner: .init(resourceObject: owner)), meta: .none, links: .none)
@@ -141,4 +164,6 @@ public typealias House = ExampleEntity<HouseDescription>
 
 public typealias SingleDogDocument = JSONAPI.Document<SingleResourceBody<Dog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, BasicJSONAPIError<String>>
 
+public typealias MutableDogDocument = JSONAPI.Document<SingleResourceBody<MutableDog>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, BasicJSONAPIError<String>>
+
 public typealias BatchPeopleDocument = JSONAPI.Document<ManyResourceBody<Person>, NoMetadata, NoLinks, Include2<Dog, House>, NoAPIDescription, BasicJSONAPIError<String>>

JSONAPI.playground/contents.xcplayground

@@ -6,5 +6,6 @@
         <page name='Full Client &amp; Server Example'/>
         <page name='Full Document Verbose Generation'/>
         <page name='Sparse Fieldsets Example'/>
+        <page name='PATCHing'/>
     </pages>
 </playground>

JSONAPI.podspec

@@ -16,7 +16,7 @@ Pod::Spec.new do |spec|
   #
 
   spec.name         = "MP-JSONAPI"
-  spec.version      = "2.3.0"
+  spec.version      = "2.5.0"
   spec.summary      = "Swift Codable JSON API framework."
 
   # This description is used to generate tags and improve search results.

README.md

@@ -16,12 +16,13 @@ See the JSON API Spec here: https://jsonapi.org/format/
 - [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)
+- [PATCH Example](https://colab.research.google.com/drive/16KY-0BoLQKiSUh9G7nYmHzB8b2vhXA2U)
 
 ### Serverside
 - [GET Example](https://colab.research.google.com/drive/1krbhzSfz8mwkBTQQnKUZJLEtYsJKSfYX)
 - [POST Example](https://colab.research.google.com/drive/1z3n70LwRY7vLIgbsMghvnfHA67QiuqpQ)
 
-### Combined
+### Client+Server
 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
@@ -76,6 +77,9 @@ This library works well when used by both the server responsible for serializati
 		- [Sparse Fieldsets](#sparse-fieldsets)
 			- [Supporting Sparse Fieldset Encoding](#supporting-sparse-fieldset-encoding)
 			- [Sparse Fieldset `typealias` comparisons](#sparse-fieldset-typealias-comparisons)
+		- [Replacing and Tapping Attributes/Relationships](#replacing-and-tapping-attributesrelationships)
+			- [Tapping](#tapping)
+			- [Replacing](#replacing)
 		- [Custom Attribute or Relationship Key Mapping](#custom-attribute-or-relationship-key-mapping)
 		- [Custom Attribute Encode/Decode](#custom-attribute-encodedecode)
 		- [Meta-Attributes](#meta-attributes)
@@ -569,6 +573,35 @@ In order to support sparse fieldsets (which are encode-only), the following comp
 typealias SparseDocument<PrimaryResourceBody: JSONAPI.EncodableResourceBody, IncludeType: JSONAPI.Include> = JSONAPI.Document<PrimaryResourceBody, NoMetadata, NoLinks, IncludeType, NoAPIDescription, BasicJSONAPIError<String>>
 ```
 
+### Replacing and Tapping Attributes/Relationships
+When you are working with an immutable Resource Object, it can be useful to replace its attributes or relationships. As a client, you might receive a resource from the server, update something, and then send the server a PATCH request.
+
+`ResourceObject` is immutable, but you can create a new copy of a `ResourceObject` having updated attributes or relationships.
+
+#### Tapping
+If your `Attributes` or `Relationships` struct is mutable (i.e. its properties are `var`s) then you may find `ResourceObject`'s `tappingAttributes()` and `tappingRelationships()` functions useful. For both, you pass a function that takes an `inout` copy of the respective object or value that you can mutate. The mutated value is then used to create a new `ResourceObject`.
+
+For example, to take a hypothetical `Dog` resource object and change the name attribute:
+```swift
+let resourceObject = Dog(...)
+
+let newResourceObject = resourceObject
+	.tappingAttributes { $0.name = .init(value: "Charlie") }
+```
+
+#### Replacing
+If your `Attributes` or `Relationships` struct is immutable (i.e. its properties are `let`s) then you may find `ResourceObject`'s `replacingAttributes()` and `replacingRelationships()` functions useful. For both, you pass a function that takes the current attributes or relationships and you return a new value. The new value is then used to create a new `ResourceObject`.
+
+For example, to take a hypothetical `Dog` resource object and change the name attribute:
+```swift
+let resourceObject = Dog(...)
+
+let newResourceObject = resourceObject
+	.replacingAttributes { _ in
+		return Dog.Attributes(name: .init(value: "Charlie"))
+}
+```
+
 ### 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:
 ```swift

Sources/JSONAPI/Document/Document.swift

@@ -414,3 +414,137 @@ extension Document.Body.Data: CustomStringConvertible {
 		return "primary: \(String(describing: primary)), includes: \(String(describing: includes)), meta: \(String(describing: meta)), links: \(String(describing: links))"
 	}
 }
+
+// MARK: - Error and Success Document Types
+
+extension Document {
+    /// A Document that only supports error bodies. This is useful if you wish to pass around a
+    /// Document type but you wish to constrain it to error values.
+    @dynamicMemberLookup
+    public struct ErrorDocument: EncodableJSONAPIDocument {
+        public var body: Document.Body { return document.body }
+
+        private let document: Document
+
+        public init(apiDescription: APIDescription, errors: [Error], meta: MetaType? = nil, links: LinksType? = nil) {
+            document = .init(apiDescription: apiDescription, errors: errors, meta: meta, links: links)
+        }
+
+        public func encode(to encoder: Encoder) throws {
+            var container = encoder.singleValueContainer()
+
+            try container.encode(document)
+        }
+
+        public subscript<T>(dynamicMember path: KeyPath<Document, T>) -> T {
+            return document[keyPath: path]
+        }
+
+        public static func ==(lhs: Document, rhs: ErrorDocument) -> Bool {
+            return lhs == rhs.document
+        }
+    }
+
+    /// A Document that only supports success bodies. This is useful if you wish to pass around a
+    /// Document type but you wish to constrain it to success values.
+    @dynamicMemberLookup
+    public struct SuccessDocument: EncodableJSONAPIDocument {
+        public var body: Document.Body { return document.body }
+
+        private let document: Document
+
+        public init(apiDescription: APIDescription,
+                    body: PrimaryResourceBody,
+                    includes: Includes<Include>,
+                    meta: MetaType,
+                    links: LinksType) {
+            document = .init(apiDescription: apiDescription,
+                             body: body,
+                             includes: includes,
+                             meta: meta,
+                             links: links)
+        }
+
+        public func encode(to encoder: Encoder) throws {
+            var container = encoder.singleValueContainer()
+
+            try container.encode(document)
+        }
+
+        public subscript<T>(dynamicMember path: KeyPath<Document, T>) -> T {
+            return document[keyPath: path]
+        }
+
+        public static func ==(lhs: Document, rhs: SuccessDocument) -> Bool {
+            return lhs == rhs.document
+        }
+    }
+}
+
+extension Document.ErrorDocument: Decodable, JSONAPIDocument
+    where PrimaryResourceBody: ResourceBody, IncludeType: Decodable {
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.singleValueContainer()
+
+        document = try container.decode(Document.self)
+
+        guard document.body.isError else {
+            throw JSONAPIDocumentDecodingError.foundSuccessDocumentWhenExpectingError
+        }
+    }
+}
+
+extension Document.SuccessDocument: Decodable, JSONAPIDocument
+    where PrimaryResourceBody: ResourceBody, IncludeType: Decodable {
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.singleValueContainer()
+
+        document = try container.decode(Document.self)
+
+        guard !document.body.isError else {
+            throw JSONAPIDocumentDecodingError.foundErrorDocumentWhenExpectingSuccess
+        }
+    }
+}
+
+extension Document.SuccessDocument where IncludeType == NoIncludes {
+    /// Create a new Document with the given includes.
+    public func including<I: JSONAPI.Include>(_ includes: Includes<I>) -> Document<PrimaryResourceBody, MetaType, LinksType, I, APIDescription, Error>.SuccessDocument {
+        // Note that if IncludeType is NoIncludes, then we allow anything
+        // to be included, but if IncludeType already specifies a type
+        // of thing to be expected then we lock that down.
+        // See: Document.including() where IncludeType: _Poly1
+        switch document.body {
+        case .data(let data):
+            return .init(apiDescription: document.apiDescription,
+                         body: data.primary,
+                         includes: includes,
+                         meta: data.meta,
+                         links: data.links)
+        case .errors:
+            fatalError("SuccessDocument cannot end up in an error state")
+        }
+    }
+}
+
+// extending where _Poly1 means all non-zero _Poly arities are included
+extension Document.SuccessDocument where IncludeType: _Poly1 {
+    /// Create a new Document adding the given includes. This does not
+    /// remove existing includes; it is additive.
+    public func including(_ includes: Includes<IncludeType>) -> Document.SuccessDocument {
+        // Note that if IncludeType is NoIncludes, then we allow anything
+        // to be included, but if IncludeType already specifies a type
+        // of thing to be expected then we lock that down.
+        // See: Document.including() where IncludeType == NoIncludes
+        switch document.body {
+        case .data(let data):
+            return .init(apiDescription: document.apiDescription,
+                         body: data.primary,
+                         includes: data.includes + includes,
+                         meta: data.meta,
+                         links: data.links)
+        case .errors:
+            fatalError("SuccessDocument cannot end up in an error state")
+        }
+    }
+}

Sources/JSONAPI/Document/DocumentDecodingError.swift

@@ -0,0 +1,11 @@
+//
+//  DocumentDecodingErro.swift
+//  
+//
+//  Created by Mathew Polzin on 10/20/19.
+//
+
+public enum JSONAPIDocumentDecodingError: Swift.Error {
+    case foundErrorDocumentWhenExpectingSuccess
+    case foundSuccessDocumentWhenExpectingError
+}

Sources/JSONAPI/Resource/Resource Object/ResourceObject+Replacing.swift

@@ -0,0 +1,74 @@
+//
+//  ResourceObject+Replacing.swift
+//  JSONAPI
+//
+//  Created by Mathew Polzin on 10/12/19.
+//
+
+public extension JSONAPI.ResourceObject {
+    /// Return a new `ResourceObject`, having replaced `self`'s
+    /// `attributes` with the attributes returned by the given
+    /// replacement function.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - replacement: A function that takes the existing `attributes` and returns the replacement.
+    func replacingAttributes(_ replacement: (Description.Attributes) -> Description.Attributes) -> Self {
+        return Self(id: id,
+                    attributes: replacement(attributes),
+                    relationships: relationships,
+                    meta: meta,
+                    links: links)
+    }
+
+    /// Return a new `ResourceObject`, having updated `self`'s
+    /// `attributes` with the tap function given.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - tap: A function that takes a copy of the existing `attributes` and mutates them.
+    func tappingAttributes(_ tap: (inout Description.Attributes) -> Void) -> Self {
+        var newAttributes = attributes
+        tap(&newAttributes)
+        return Self(id: id,
+                    attributes: newAttributes,
+                    relationships: relationships,
+                    meta: meta,
+                    links: links)
+    }
+
+    /// Return a new `ResourceObject`, having replaced `self`'s
+    /// `relationships` with the `relationships` returned by the given
+    /// replacement function.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - replacement: A function that takes the existing relationships and returns the replacement.
+    func replacingRelationships(_ replacement: (Description.Relationships) -> Description.Relationships) -> Self {
+        return Self(id: id,
+                    attributes: attributes,
+                    relationships: replacement(relationships),
+                    meta: meta,
+                    links: links)
+    }
+
+    /// Return a new `ResourceObject`, having updated `self`'s
+    /// `relationships` with the tap function given.
+    ///
+    /// - important: `self` is not mutated. A copy of self is returned.
+    ///
+    /// - parameters:
+    ///     - tap: A function that takes a copy of the existing `relationships` and mutates them.
+    func tappingRelationships(_ tap: (inout Description.Relationships) -> Void) -> Self {
+        var newRelationships = relationships
+        tap(&newRelationships)
+        return Self(id: id,
+                    attributes: attributes,
+                    relationships: newRelationships,
+                    meta: meta,
+                    links: links)
+    }
+}

Tests/JSONAPITests/Document/DocumentTests.swift

@@ -23,6 +23,7 @@ class DocumentTests: XCTestCase {
             XCTAssert(Doc.Error.self == UnknownJSONAPIError.self)
         }
 
+        // Document
         test(JSONAPI.Document<
             NoResourceBody,
             NoMetadata,
@@ -37,6 +38,35 @@ class DocumentTests: XCTestCase {
                 meta: .none,
                 links: .none
         ))
+
+        // Document.SuccessDocument
+        test(JSONAPI.Document<
+            NoResourceBody,
+            NoMetadata,
+            NoLinks,
+            NoIncludes,
+            NoAPIDescription,
+            UnknownJSONAPIError
+            >.SuccessDocument(
+                apiDescription: .none,
+                body: .none,
+                includes: .none,
+                meta: .none,
+                links: .none
+        ))
+
+        // Document.ErrorDocument
+        test(JSONAPI.Document<
+            NoResourceBody,
+            NoMetadata,
+            NoLinks,
+            NoIncludes,
+            NoAPIDescription,
+            UnknownJSONAPIError
+            >.ErrorDocument(
+                apiDescription: .none,
+                errors: []
+        ))
     }
 
 	func test_singleDocumentNull() {
@@ -51,11 +81,34 @@ class DocumentTests: XCTestCase {
 		XCTAssertEqual(document.body.includes?.count, 0)
 		XCTAssertEqual(document.body.links, NoLinks())
 		XCTAssertEqual(document.apiDescription, .none)
+
+        // SuccessDocument
+        let document2 = decoded(type: Document<SingleResourceBody<Article?>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.SuccessDocument.self,
+                                data: single_document_null)
+
+        XCTAssert(document == document2)
+
+        XCTAssertFalse(document2.body.isError)
+        XCTAssertNil(document2.body.errors)
+        XCTAssertNotNil(document2.body.primaryResource)
+        XCTAssertEqual(document2.body.meta, NoMetadata())
+        XCTAssertNil(document2.body.primaryResource?.value)
+        XCTAssertEqual(document2.body.includes?.count, 0)
+        XCTAssertEqual(document2.body.links, NoLinks())
+        XCTAssertEqual(document2.apiDescription, .none)
+
+        // ErrorDocument
+        XCTAssertThrowsError(try JSONDecoder().decode(Document<SingleResourceBody<Article?>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.ErrorDocument.self,
+                                                       from: single_document_null))
 	}
 
 	func test_singleDocumentNull_encode() {
 		test_DecodeEncodeEquality(type: Document<SingleResourceBody<Article?>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.self,
 								  data: single_document_null)
+
+        // SuccessDocument
+        test_DecodeEncodeEquality(type: Document<SingleResourceBody<Article?>, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.SuccessDocument.self,
+                                  data: single_document_null)
 	}
 
 	func test_singleDocumentNullWithAPIDescription() {
@@ -94,6 +147,14 @@ extension DocumentTests {
 	func test_errorDocumentFailsWithNoAPIDescription() {
 		XCTAssertThrowsError(try JSONDecoder().decode(Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, TestAPIDescription, UnknownJSONAPIError>.self,
 													  from: error_document_no_metadata))
+
+        // SuccessDocument
+        XCTAssertThrowsError(try JSONDecoder().decode(Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, TestAPIDescription, UnknownJSONAPIError>.SuccessDocument.self,
+                                                      from: error_document_no_metadata))
+
+        // ErrorDocument
+        XCTAssertThrowsError(try JSONDecoder().decode(Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, TestAPIDescription, UnknownJSONAPIError>.ErrorDocument.self,
+                                                      from: error_document_no_metadata))
 	}
 
 	func test_unknownErrorDocumentNoMeta() {
@@ -115,6 +176,32 @@ extension DocumentTests {
 		XCTAssertEqual(errors.0, document.body.errors)
 		XCTAssertEqual(errors.0[0], .unknown)
 		XCTAssertEqual(errors.meta, NoMetadata())
+
+        // SuccessDocument
+        XCTAssertThrowsError(try JSONDecoder().decode(Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.SuccessDocument.self,
+                                                      from: error_document_no_metadata))
+
+        // ErrorDocument
+        let document2 = decoded(type: Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.ErrorDocument.self,
+                                data: error_document_no_metadata)
+
+        XCTAssert(document == document2)
+
+        XCTAssertTrue(document2.body.isError)
+        XCTAssertEqual(document2.body.meta, NoMetadata())
+        XCTAssertNil(document2.body.data)
+        XCTAssertNil(document2.body.primaryResource)
+        XCTAssertNil(document2.body.includes)
+
+        guard case let .errors(errors2) = document2.body else {
+            XCTFail("Needed body to be in errors case but it was not.")
+            return
+        }
+
+        XCTAssertEqual(errors2.0.count, 1)
+        XCTAssertEqual(errors2.0, document2.body.errors)
+        XCTAssertEqual(errors2.0[0], .unknown)
+        XCTAssertEqual(errors2.meta, NoMetadata())
 	}
 
 	func test_unknownErrorDocumentAddIncludingType() {
@@ -620,6 +707,27 @@ extension DocumentTests {
 		XCTAssertEqual(documentWithIncludes.body.includes?[Author.self], [author])
 	}
 
+    func test_singleSuccessDocumentNoIncludesAddIncludingType() {
+        // NOTE distinct from above for being Document.SuccessDocument
+        let author = Author(id: "1",
+                            attributes: .none,
+                            relationships: .none,
+                            meta: .none,
+                            links: .none)
+
+        let document = decoded(type: Document<NoResourceBody, NoMetadata, NoLinks, NoIncludes, NoAPIDescription, UnknownJSONAPIError>.SuccessDocument.self,
+                               data: single_document_no_includes)
+
+        let documentWithIncludes = document.including(Includes<Include1<Author>>(values: [.init(author)]))
+
+        XCTAssert(type(of: documentWithIncludes) == Document<NoResourceBody, NoMetadata, NoLinks, Include1<Author>, NoAPIDescription, UnknownJSONAPIError>.SuccessDocument.self)
+        XCTAssertEqual(document.body.errors, documentWithIncludes.body.errors)
+        XCTAssertEqual(document.body.meta, documentWithIncludes.body.meta)
+        XCTAssertEqual(document.body.links, documentWithIncludes.body.links)
+        XCTAssertEqual(document.body.includes, Includes<NoIncludes>.none)
+        XCTAssertEqual(documentWithIncludes.body.includes?[Author.self], [author])
+    }
+
 	func test_singleDocumentNoIncludesWithAPIDescription() {
 		let document = decoded(type: Document<SingleResourceBody<Article>, NoMetadata, NoLinks, NoIncludes, TestAPIDescription, UnknownJSONAPIError>.self,
 							   data: single_document_no_includes_with_api_description)
@@ -848,6 +956,31 @@ extension DocumentTests {
 		XCTAssertEqual(documentWithIncludes.body.includes?[Author.self], [existingAuthor, newAuthor])
 	}
 
+    func test_singleSuccessDocumentSomeIncludesAddIncludes() {
+        // NOTE distinct from above for being Document.SuccessDocument
+        let existingAuthor = Author(id: "33",
+                                    attributes: .none,
+                                    relationships: .none,
+                                    meta: .none,
+                                    links: .none)
+
+        let newAuthor = Author(id: "1",
+                               attributes: .none,
+                               relationships: .none,
+                               meta: .none,
+                               links: .none)
+
+        let document = decoded(type: Document<SingleResourceBody<Article>, NoMetadata, NoLinks, Include1<Author>, NoAPIDescription, UnknownJSONAPIError>.SuccessDocument.self,
+                               data: single_document_some_includes)
+
+        let documentWithIncludes = document.including(.init(values: [.init(newAuthor)]))
+
+        XCTAssertEqual(document.body.errors, documentWithIncludes.body.errors)
+        XCTAssertEqual(document.body.meta, documentWithIncludes.body.meta)
+        XCTAssertEqual(document.body.links, documentWithIncludes.body.links)
+        XCTAssertEqual(documentWithIncludes.body.includes?[Author.self], [existingAuthor, newAuthor])
+    }
+
 	func test_singleDocumentSomeIncludesWithAPIDescription() {
 		let document = decoded(type: Document<SingleResourceBody<Article>, NoMetadata, NoLinks, Include1<Author>, TestAPIDescription, UnknownJSONAPIError>.self,
 							   data: single_document_some_includes_with_api_description)

Tests/JSONAPITests/ResourceObject/ResourceObject+ReplacingTests.swift

@@ -0,0 +1,155 @@
+//
+//  ResourceObject+ReplacingTests.swift
+//  JSONAPITests
+//
+//  Created by Mathew Polzin on 10/12/19.
+//
+
+import XCTest
+import JSONAPI
+
+final class ResourceObjectReplacingTests: XCTestCase {
+    func test_replaceMutableAttributes() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .replacingAttributes {
+                var newAttributes = $0
+                newAttributes.name = .init(value: "Matt 2")
+                return newAttributes
+        }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_tapMutableAttributes() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .tappingAttributes { $0.name = .init(value: "Matt 2") }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_replaceImmutableAttributes() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .replacingAttributes {
+                return .init(name: $0.name.map { $0 + " 2" })
+        }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_tapImmutableAttributes() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .tappingAttributes { $0 = .init(name: $0.name.map { $0 + " 2" }) }
+
+        XCTAssertEqual(testResource.name, "Matt")
+        XCTAssertEqual(mutatedResource.name, "Matt 2")
+    }
+
+    func test_replaceMutableRelationships() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .replacingRelationships {
+                var newRelationships = $0
+                newRelationships.other = .init(id: .init(rawValue: "3"))
+                return newRelationships
+        }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+
+    func test_tapMutableRelationships() {
+        let testResource = MutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                           relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                           meta: .none,
+                                           links: .none)
+
+        let mutatedResource = testResource
+            .tappingRelationships { $0.other = .init(id: .init(rawValue: "3")) }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+
+    func test_replaceImmutableRelationships() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .replacingRelationships { _ in
+                return .init(other: .init(id: .init(rawValue: "3")))
+        }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+
+    func test_tapImmutableRelationships() {
+        let testResource = ImmutableTestType(attributes: .init(name: .init(value: "Matt")),
+                                             relationships: .init(other: .init(id: .init(rawValue: "2"))),
+                                             meta: .none,
+                                             links: .none)
+
+        let mutatedResource = testResource
+            .tappingRelationships { $0 = .init(other: .init(id: .init(rawValue: "3"))) }
+
+        XCTAssertEqual(testResource ~> \.other, "2")
+        XCTAssertEqual(mutatedResource ~> \.other, "3")
+    }
+}
+
+private enum MutableTestDescription: JSONAPI.ResourceObjectDescription {
+    static let jsonType: String = "test"
+
+    struct Attributes: JSONAPI.Attributes {
+        var name: Attribute<String>
+    }
+
+    struct Relationships: JSONAPI.Relationships {
+        var other: ToOneRelationship<MutableTestType, NoMetadata, NoLinks>
+    }
+}
+
+private typealias MutableTestType = JSONAPI.ResourceObject<MutableTestDescription, NoMetadata, NoLinks, String>
+
+private enum ImmutableTestDescription: JSONAPI.ResourceObjectDescription {
+    static let jsonType: String = "test2"
+
+    struct Attributes: JSONAPI.Attributes {
+        let name: Attribute<String>
+    }
+
+    struct Relationships: JSONAPI.Relationships {
+        let other: ToOneRelationship<ImmutableTestType, NoMetadata, NoLinks>
+    }
+}
+
+private typealias ImmutableTestType = JSONAPI.ResourceObject<ImmutableTestDescription, NoMetadata, NoLinks, String>

Tests/JSONAPITests/XCTestManifests.swift

@@ -42,6 +42,17 @@ extension Attribute_FunctorTests {
     ]
 }
 
+extension BasicJSONAPIErrorTests {
+    // DO NOT MODIFY: This is autogenerated, use:
+    //   `swift test --generate-linuxmain`
+    // to regenerate.
+    static let __allTests__BasicJSONAPIErrorTests = [
+        ("test_decodeAFewExamples", test_decodeAFewExamples),
+        ("test_definedFields", test_definedFields),
+        ("test_initAndEquality", test_initAndEquality),
+    ]
+}
+
 extension ComputedPropertiesTests {
     // DO NOT MODIFY: This is autogenerated, use:
     //   `swift test --generate-linuxmain`
@@ -145,6 +156,8 @@ extension DocumentTests {
         ("test_singleDocumentSomeIncludesWithMetadata_encode", test_singleDocumentSomeIncludesWithMetadata_encode),
         ("test_singleDocumentSomeIncludesWithMetadataWithAPIDescription", test_singleDocumentSomeIncludesWithMetadataWithAPIDescription),
         ("test_singleDocumentSomeIncludesWithMetadataWithAPIDescription_encode", test_singleDocumentSomeIncludesWithMetadataWithAPIDescription_encode),
+        ("test_singleSuccessDocumentNoIncludesAddIncludingType", test_singleSuccessDocumentNoIncludesAddIncludingType),
+        ("test_singleSuccessDocumentSomeIncludesAddIncludes", test_singleSuccessDocumentSomeIncludesAddIncludes),
         ("test_sparseIncludeFullPrimaryResource", test_sparseIncludeFullPrimaryResource),
         ("test_sparseIncludeSparsePrimaryResource", test_sparseIncludeSparsePrimaryResource),
         ("test_sparsePrimaryResource", test_sparsePrimaryResource),
@@ -196,6 +209,21 @@ extension EmptyObjectDecoderTests {
     ]
 }
 
+extension GenericJSONAPIErrorTests {
+    // DO NOT MODIFY: This is autogenerated, use:
+    //   `swift test --generate-linuxmain`
+    // to regenerate.
+    static let __allTests__GenericJSONAPIErrorTests = [
+        ("test_decodeKnown", test_decodeKnown),
+        ("test_decodeUnknown", test_decodeUnknown),
+        ("test_definedFields", test_definedFields),
+        ("test_encode", test_encode),
+        ("test_encodeUnknown", test_encodeUnknown),
+        ("test_initAndEquality", test_initAndEquality),
+        ("test_payloadAccess", test_payloadAccess),
+    ]
+}
+
 extension IncludedTests {
     // DO NOT MODIFY: This is autogenerated, use:
     //   `swift test --generate-linuxmain`
@@ -205,6 +233,8 @@ extension IncludedTests {
         ("test_ComboSparseAndFullIncludeTypes", test_ComboSparseAndFullIncludeTypes),
         ("test_EightDifferentIncludes", test_EightDifferentIncludes),
         ("test_EightDifferentIncludes_encode", test_EightDifferentIncludes_encode),
+        ("test_ElevenDifferentIncludes", test_ElevenDifferentIncludes),
+        ("test_ElevenDifferentIncludes_encode", test_ElevenDifferentIncludes_encode),
         ("test_FiveDifferentIncludes", test_FiveDifferentIncludes),
         ("test_FiveDifferentIncludes_encode", test_FiveDifferentIncludes_encode),
         ("test_FourDifferentIncludes", test_FourDifferentIncludes),
@@ -323,6 +353,22 @@ extension ResourceBodyTests {
     ]
 }
 
+extension ResourceObjectReplacingTests {
+    // DO NOT MODIFY: This is autogenerated, use:
+    //   `swift test --generate-linuxmain`
+    // to regenerate.
+    static let __allTests__ResourceObjectReplacingTests = [
+        ("test_replaceImmutableAttributes", test_replaceImmutableAttributes),
+        ("test_replaceImmutableRelationships", test_replaceImmutableRelationships),
+        ("test_replaceMutableAttributes", test_replaceMutableAttributes),
+        ("test_replaceMutableRelationships", test_replaceMutableRelationships),
+        ("test_tapImmutableAttributes", test_tapImmutableAttributes),
+        ("test_tapImmutableRelationships", test_tapImmutableRelationships),
+        ("test_tapMutableAttributes", test_tapMutableAttributes),
+        ("test_tapMutableRelationships", test_tapMutableRelationships),
+    ]
+}
+
 extension ResourceObjectTests {
     // DO NOT MODIFY: This is autogenerated, use:
     //   `swift test --generate-linuxmain`
@@ -442,16 +488,19 @@ public func __allTests() -> [XCTestCaseEntry] {
         testCase(APIDescriptionTests.__allTests__APIDescriptionTests),
         testCase(AttributeTests.__allTests__AttributeTests),
         testCase(Attribute_FunctorTests.__allTests__Attribute_FunctorTests),
+        testCase(BasicJSONAPIErrorTests.__allTests__BasicJSONAPIErrorTests),
         testCase(ComputedPropertiesTests.__allTests__ComputedPropertiesTests),
         testCase(CustomAttributesTests.__allTests__CustomAttributesTests),
         testCase(DocumentTests.__allTests__DocumentTests),
         testCase(EmptyObjectDecoderTests.__allTests__EmptyObjectDecoderTests),
+        testCase(GenericJSONAPIErrorTests.__allTests__GenericJSONAPIErrorTests),
         testCase(IncludedTests.__allTests__IncludedTests),
         testCase(LinksTests.__allTests__LinksTests),
         testCase(NonJSONAPIRelatableTests.__allTests__NonJSONAPIRelatableTests),
         testCase(PolyProxyTests.__allTests__PolyProxyTests),
         testCase(RelationshipTests.__allTests__RelationshipTests),
         testCase(ResourceBodyTests.__allTests__ResourceBodyTests),
+        testCase(ResourceObjectReplacingTests.__allTests__ResourceObjectReplacingTests),
         testCase(ResourceObjectTests.__allTests__ResourceObjectTests),
         testCase(SparseFieldEncoderTests.__allTests__SparseFieldEncoderTests),
         testCase(SparseFieldsetTests.__allTests__SparseFieldsetTests),