Align optional decode with Aeson

A missing key in an embedded type should be a failure.

Argo.xcodeproj/project.pbxproj

@@ -107,6 +107,15 @@
 		EA47BB591AFC5E65002D2CCD /* user_without_key.json in Resources */ = {isa = PBXBuildFile; fileRef = EA47BB581AFC5E65002D2CCD /* user_without_key.json */; };
 		EA47BB5A1AFC5E65002D2CCD /* user_without_key.json in Resources */ = {isa = PBXBuildFile; fileRef = EA47BB581AFC5E65002D2CCD /* user_without_key.json */; };
 		EA4EAF7319DD96330036AE0D /* types_fail_embedded.json in Resources */ = {isa = PBXBuildFile; fileRef = EA4EAF7219DD96330036AE0D /* types_fail_embedded.json */; };
+		EA6600ED1D8C648F0032103D /* EmbeddedDecodingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = EA6600EC1D8C648F0032103D /* EmbeddedDecodingTests.swift */; };
+		EA6600EE1D8C648F0032103D /* EmbeddedDecodingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = EA6600EC1D8C648F0032103D /* EmbeddedDecodingTests.swift */; };
+		EA6600EF1D8C648F0032103D /* EmbeddedDecodingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = EA6600EC1D8C648F0032103D /* EmbeddedDecodingTests.swift */; };
+		EA6600F11D8C651E0032103D /* location_post.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6600F01D8C651E0032103D /* location_post.json */; };
+		EA6600F21D8C651E0032103D /* location_post.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6600F01D8C651E0032103D /* location_post.json */; };
+		EA6600F31D8C651E0032103D /* location_post.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6600F01D8C651E0032103D /* location_post.json */; };
+		EA6600F51D8C65940032103D /* bad_location_post.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6600F41D8C65940032103D /* bad_location_post.json */; };
+		EA6600F61D8C65940032103D /* bad_location_post.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6600F41D8C65940032103D /* bad_location_post.json */; };
+		EA6600F71D8C65940032103D /* bad_location_post.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6600F41D8C65940032103D /* bad_location_post.json */; };
 		EA6DD69C1AB383FB00CA3A5B /* PerformanceTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = EA6DD69B1AB383FB00CA3A5B /* PerformanceTests.swift */; };
 		EA6DD69D1AB383FB00CA3A5B /* PerformanceTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = EA6DD69B1AB383FB00CA3A5B /* PerformanceTests.swift */; };
 		EA6DD69F1AB384C700CA3A5B /* big_data.json in Resources */ = {isa = PBXBuildFile; fileRef = EA6DD69E1AB384C700CA3A5B /* big_data.json */; };
@@ -296,6 +305,9 @@
 		EA47BB551AFC5DAC002D2CCD /* user_with_bad_type.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = user_with_bad_type.json; sourceTree = "<group>"; };
 		EA47BB581AFC5E65002D2CCD /* user_without_key.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = user_without_key.json; sourceTree = "<group>"; };
 		EA4EAF7219DD96330036AE0D /* types_fail_embedded.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = types_fail_embedded.json; sourceTree = "<group>"; };
+		EA6600EC1D8C648F0032103D /* EmbeddedDecodingTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = EmbeddedDecodingTests.swift; sourceTree = "<group>"; };
+		EA6600F01D8C651E0032103D /* location_post.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = location_post.json; sourceTree = "<group>"; };
+		EA6600F41D8C65940032103D /* bad_location_post.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = bad_location_post.json; sourceTree = "<group>"; };
 		EA6DD69B1AB383FB00CA3A5B /* PerformanceTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = PerformanceTests.swift; sourceTree = "<group>"; };
 		EA6DD69E1AB384C700CA3A5B /* big_data.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = big_data.json; sourceTree = "<group>"; };
 		EABDF6891A9CD46100B6CC83 /* SwiftDictionaryDecodingTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = SwiftDictionaryDecodingTests.swift; sourceTree = "<group>"; };
@@ -548,6 +560,8 @@
 				EA6DD69E1AB384C700CA3A5B /* big_data.json */,
 				EA47BB581AFC5E65002D2CCD /* user_without_key.json */,
 				EA47BB551AFC5DAC002D2CCD /* user_with_bad_type.json */,
+				EA6600F01D8C651E0032103D /* location_post.json */,
+				EA6600F41D8C65940032103D /* bad_location_post.json */,
 			);
 			path = JSON;
 			sourceTree = "<group>";
@@ -565,6 +579,7 @@
 				EA6DD69B1AB383FB00CA3A5B /* PerformanceTests.swift */,
 				EA47BB521AFC5B76002D2CCD /* DecodedTests.swift */,
 				EA1200CA1BAB5CBA006DDBD8 /* RawRepresentableTests.swift */,
+				EA6600EC1D8C648F0032103D /* EmbeddedDecodingTests.swift */,
 			);
 			path = Tests;
 			sourceTree = "<group>";
@@ -866,11 +881,13 @@
 				809755061BADF3ED00C409E6 /* root_object.json in Resources */,
 				809755021BADF3ED00C409E6 /* post_bad_comments.json in Resources */,
 				809755001BADF3ED00C409E6 /* post_no_comments.json in Resources */,
+				EA6600F31D8C651E0032103D /* location_post.json in Resources */,
 				809754F91BADF3ED00C409E6 /* user_with_email.json in Resources */,
 				8097550A1BADF3F200C409E6 /* types.plist in Resources */,
 				809755041BADF3ED00C409E6 /* types_fail_embedded.json in Resources */,
 				809755051BADF3ED00C409E6 /* array_root.json in Resources */,
 				809754FC1BADF3ED00C409E6 /* url.json in Resources */,
+				EA6600F71D8C65940032103D /* bad_location_post.json in Resources */,
 				809755091BADF3ED00C409E6 /* user_without_key.json in Resources */,
 				809754FF1BADF3ED00C409E6 /* comment.json in Resources */,
 			);
@@ -906,11 +923,13 @@
 				4D5F6DD91B3832C200D79B25 /* user_with_nested_name.json in Resources */,
 				EABDF6911A9CD4EA00B6CC83 /* types.plist in Resources */,
 				EAD9FB0A19D214AA0031E006 /* user_without_email.json in Resources */,
+				EA6600F11D8C651E0032103D /* location_post.json in Resources */,
 				EAD9FB0619D2143A0031E006 /* user_with_email.json in Resources */,
 				EAD9FB0B19D214AA0031E006 /* TemplateIcon2x.png in Resources */,
 				EA47BB591AFC5E65002D2CCD /* user_without_key.json in Resources */,
 				EA395DC41A52F8EB00EB607E /* array_root.json in Resources */,
 				F8E33FA51A51E0C20025A6E5 /* post_bad_comments.json in Resources */,
+				EA6600F51D8C65940032103D /* bad_location_post.json in Resources */,
 				EAD9FB1419D30ED00031E006 /* comment.json in Resources */,
 				F802D4C61A5EE2D5005E236C /* url.json in Resources */,
 			);
@@ -939,11 +958,13 @@
 				4D5F6DDA1B3832C200D79B25 /* user_with_nested_name.json in Resources */,
 				EABDF6921A9CD4EA00B6CC83 /* types.plist in Resources */,
 				F8EF756E1A4CEC7100BDCC2D /* user_without_email.json in Resources */,
+				EA6600F21D8C651E0032103D /* location_post.json in Resources */,
 				F8EF756D1A4CEC7100BDCC2D /* user_with_email.json in Resources */,
 				F8EF756F1A4CEC7100BDCC2D /* TemplateIcon2x.png in Resources */,
 				EA47BB5A1AFC5E65002D2CCD /* user_without_key.json in Resources */,
 				EA395DC51A52F8EE00EB607E /* array_root.json in Resources */,
 				EA395DC21A5209C000EB607E /* post_bad_comments.json in Resources */,
+				EA6600F61D8C65940032103D /* bad_location_post.json in Resources */,
 				F8EF75701A4CEC7100BDCC2D /* comment.json in Resources */,
 				F802D4C71A5EE2D5005E236C /* url.json in Resources */,
 			);
@@ -1007,6 +1028,7 @@
 				F8C592841CB726FF007C5ABC /* Booleans.swift in Sources */,
 				809754EA1BADF3E400C409E6 /* OptionalPropertyDecodingTests.swift in Sources */,
 				809754F81BADF3E400C409E6 /* URL.swift in Sources */,
+				EA6600EF1D8C648F0032103D /* EmbeddedDecodingTests.swift in Sources */,
 				809754F41BADF3E400C409E6 /* User.swift in Sources */,
 				809754EC1BADF3E400C409E6 /* TypeTests.swift in Sources */,
 				809754E81BADF3E400C409E6 /* PListDecodingTests.swift in Sources */,
@@ -1084,6 +1106,7 @@
 				F8C592821CB726FB007C5ABC /* Booleans.swift in Sources */,
 				EAD9FB0219D211C10031E006 /* Post.swift in Sources */,
 				EABDF6941A9CD4FC00B6CC83 /* PListDecodingTests.swift in Sources */,
+				EA6600ED1D8C648F0032103D /* EmbeddedDecodingTests.swift in Sources */,
 				EAD9FB1819D49A3E0031E006 /* TestModel.swift in Sources */,
 				EAD9FB0E19D215570031E006 /* OptionalPropertyDecodingTests.swift in Sources */,
 				EA47BB531AFC5B76002D2CCD /* DecodedTests.swift in Sources */,
@@ -1135,6 +1158,7 @@
 				F8C592831CB726FE007C5ABC /* Booleans.swift in Sources */,
 				F8EF756B1A4CEC6400BDCC2D /* EmbeddedJSONDecodingTests.swift in Sources */,
 				EABDF6951A9CD4FC00B6CC83 /* PListDecodingTests.swift in Sources */,
+				EA6600EE1D8C648F0032103D /* EmbeddedDecodingTests.swift in Sources */,
 				F8EF75751A4CEC7800BDCC2D /* TestModel.swift in Sources */,
 				F8EF75741A4CEC7800BDCC2D /* Post.swift in Sources */,
 				EA47BB541AFC5B76002D2CCD /* DecodedTests.swift in Sources */,

Argo/Operators/Decode.swift

@@ -33,7 +33,7 @@ public func <| <A: Decodable>(json: JSON, key: String) -> Decoded<A> where A ==
              the decode operation
 */
 public func <|? <A: Decodable>(json: JSON, key: String) -> Decoded<A?> where A == A.DecodedType {
-  return .optional(json <| [key])
+  return json <|? [key]
 }
 
 /**
@@ -71,7 +71,10 @@ public func <| <A: Decodable>(json: JSON, keys: [String]) -> Decoded<A> where A
              the decode operation
 */
 public func <|? <A: Decodable>(json: JSON, keys: [String]) -> Decoded<A?> where A == A.DecodedType {
-  return .optional(json <| keys)
+  switch flatReduce(keys, initial: json, combine: decodedJSON) {
+  case .failure: return .success(.none)
+  case .success(let x): return A.decode(x) >>- { .success(.some($0)) }
+  }
 }
 
 /**
@@ -108,7 +111,7 @@ public func <|| <A: Decodable>(json: JSON, key: String) -> Decoded<[A]> where A
              failure of the decode operation
 */
 public func <||? <A: Decodable>(json: JSON, key: String) -> Decoded<[A]?> where A == A.DecodedType {
-  return .optional(json <|| [key])
+  return json <||? [key]
 }
 
 /**
@@ -148,5 +151,8 @@ public func <|| <A: Decodable>(json: JSON, keys: [String]) -> Decoded<[A]> where
              failure of the decode operation
 */
 public func <||? <A: Decodable>(json: JSON, keys: [String]) -> Decoded<[A]?> where A == A.DecodedType {
-  return .optional(json <|| keys)
+  switch flatReduce(keys, initial: json, combine: decodedJSON) {
+  case .failure: return .success(.none)
+  case .success(let value): return Array<A>.decode(value) >>- { .success(.some($0)) }
+  }
 }

Argo/Types/Decoded/Decoded.swift

@@ -31,32 +31,6 @@ public extension Decoded {
 }
 
 public extension Decoded {
-  /**
-    Convert a `Decoded` type into a `Decoded` `Optional` type.
-
-    This is useful for when a decode operation should be allowed to fail, such
-    as when decoding an optional property.
-
-    It only returns a `.Failure` case if the error is `.TypeMismatch` or
-    `.Custom`. If the error was `.MissingKey`, it converts the failure into
-    `.Success(.None)`.
-
-    - parameter x: A `Decoded` type
-
-    - returns: The `Decoded` type with a `.TypeMismatch` failure converted to
-               `.Success(.None)`
-  */
-  static func optional<T>(_ x: Decoded<T>) -> Decoded<T?> {
-    switch x {
-    case let .success(value): return .success(.some(value))
-    case .failure(.missingKey): return .success(.none)
-    case let .failure(.typeMismatch(expected, actual)):
-      return .failure(.typeMismatch(expected: expected, actual: actual))
-    case let .failure(.custom(x)): return .failure(.custom(x))
-    case let .failure(.multiple(es)): return .failure(.multiple(es))
-    }
-  }
-
   /**
     Convert an `Optional` into a `Decoded` value.
 

Argo/Types/StandardTypes.swift

@@ -173,7 +173,7 @@ public extension Optional where Wrapped: Decodable, Wrapped == Wrapped.DecodedTy
     - returns: A decoded optional `Wrapped` value
   */
   static func decode(_ json: JSON) -> Decoded<Wrapped?> {
-    return .optional(Wrapped.decode(json))
+    return Wrapped.decode(json) >>- { .success(.some($0)) }
   }
 }
 

ArgoTests/JSON/bad_location_post.json

@@ -0,0 +1,13 @@
+{
+  "id": 3,
+  "text": "A Cool story.",
+  "author": {
+    "id": 1,
+    "name": "Cool User"
+  },
+  "comments": [],
+  "location": {
+    "lat": -41.24673,
+    "lng": 72.89244
+  }
+}

ArgoTests/JSON/location_post.json

@@ -0,0 +1,14 @@
+{
+  "id": 3,
+  "text": "A Cool story.",
+  "author": {
+    "id": 1,
+    "name": "Cool User"
+  },
+  "comments": [],
+  "location": {
+    "lat": -41.24673,
+    "lng": 72.89244,
+    "title": "Cool Location"
+  }
+}

ArgoTests/Models/Post.swift

@@ -18,3 +18,37 @@ extension Post: Decodable {
       <*> json <|| "comments"
   }
 }
+
+struct LocationPost {
+  let id: Int
+  let text: String
+  let author: User
+  let comments: [Comment]
+  let location: Location?
+}
+
+extension LocationPost: Decodable {
+  static func decode(_ json: JSON) -> Decoded<LocationPost> {
+    return curry(self.init)
+      <^> json <| "id"
+      <*> json <| "text"
+      <*> json <| "author"
+      <*> json <|| "comments"
+      <*> json <|? "location"
+  }
+}
+
+struct Location {
+  let lat: Double
+  let lng: Double
+  let title: String
+}
+
+extension Location: Decodable {
+  static func decode(_ json: JSON) -> Decoded<Location> {
+    return curry(self.init)
+      <^> json <| "lat"
+      <*> json <| "lng"
+      <*> json <| "title"
+  }
+}

ArgoTests/Tests/EmbeddedDecodingTests.swift

@@ -0,0 +1,22 @@
+import XCTest
+import Argo
+
+final class EmbeddedDecodingTests: XCTestCase {
+  func testDecodeEmbeddedObject() {
+    let post: Decoded<LocationPost> = decode(json(fromFile: "location_post")!)
+
+    switch post.value {
+    case .some: XCTAssert(true)
+    case .none: XCTFail("Unexpected Failure")
+    }
+  }
+
+  func testFailOnEmbeddedObject() {
+    let post: Decoded<LocationPost> = decode(json(fromFile: "bad_location_post")!)
+
+    switch post.error {
+    case .some: XCTAssert(true)
+    case .none: XCTFail("Unexpected Success")
+    }
+  }
+}