Introduce DecodedType typealias

Introducing this typealias helps when trying to conform a non-final class to `JSONDecodable`. If we just use `Self`, we run into an issue where the compiler can't ensure that return type is correct, because the class might be subclassed. By letting classes explicitly define their decoded type, we can make the compiler happy while maintaining the ability to subclass if that's what we want. As an added benefit, we can default `DecodedType` to `Self`, which means that `structs` and `final` classes don't need to worry about changing anything from the way they are doing it now.
thoughtbot · Jan 8, 2015 · 0ad59fa · 0ad59fa
1 parent fcfe190
commit 0ad59fa
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Showing 7 changed files with 47 additions and 10 deletions.
diff --git a/Argo.xcodeproj/project.pbxproj b/Argo.xcodeproj/project.pbxproj
@@ -39,6 +39,10 @@
 		EAD9FB1A19D4B23F0031E006 /* JSONValue.swift in Sources */ = {isa = PBXBuildFile; fileRef = EAD9FB1919D4B23F0031E006 /* JSONValue.swift */; };
 		EADADCB21A5DB6F600B180EC /* EquatableSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = EADADCB11A5DB6F600B180EC /* EquatableSpec.swift */; };
 		EADADCB41A5DB7F800B180EC /* EquatableSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = EADADCB11A5DB6F600B180EC /* EquatableSpec.swift */; };
+		F802D4C31A5EE061005E236C /* NSURL.swift in Sources */ = {isa = PBXBuildFile; fileRef = F802D4C21A5EE061005E236C /* NSURL.swift */; };
+		F802D4C41A5EE172005E236C /* NSURL.swift in Sources */ = {isa = PBXBuildFile; fileRef = F802D4C21A5EE061005E236C /* NSURL.swift */; };
+		F802D4C61A5EE2D5005E236C /* url.json in Resources */ = {isa = PBXBuildFile; fileRef = F802D4C51A5EE2D5005E236C /* url.json */; };
+		F802D4C71A5EE2D5005E236C /* url.json in Resources */ = {isa = PBXBuildFile; fileRef = F802D4C51A5EE2D5005E236C /* url.json */; };
 		F862E0AA1A519D360093B028 /* JSONValue.swift in Sources */ = {isa = PBXBuildFile; fileRef = EAD9FB1919D4B23F0031E006 /* JSONValue.swift */; };
 		F862E0AB1A519D470093B028 /* TypeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = EA08313019D5EEAF003B90D7 /* TypeTests.swift */; };
 		F862E0AC1A519D520093B028 /* post_comments.json in Resources */ = {isa = PBXBuildFile; fileRef = EA08313219D5EEF2003B90D7 /* post_comments.json */; };
@@ -119,6 +123,8 @@
 		EAD9FB1719D49A3E0031E006 /* TestModel.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = TestModel.swift; path = ../../../Argo/ArgoTests/Models/TestModel.swift; sourceTree = "<group>"; };
 		EAD9FB1919D4B23F0031E006 /* JSONValue.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = JSONValue.swift; path = ../../../Argo/Argo/Globals/JSONValue.swift; sourceTree = "<group>"; };
 		EADADCB11A5DB6F600B180EC /* EquatableSpec.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = EquatableSpec.swift; sourceTree = "<group>"; };
+		F802D4C21A5EE061005E236C /* NSURL.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NSURL.swift; sourceTree = "<group>"; };
+		F802D4C51A5EE2D5005E236C /* url.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = url.json; sourceTree = "<group>"; };
 		F89335541A4CE83000B88685 /* Argo.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Argo.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		F893355E1A4CE83000B88685 /* Argo-MacTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = "Argo-MacTests.xctest"; sourceTree = BUILT_PRODUCTS_DIR; };
 		F893356D1A4CE8FC00B88685 /* Argo.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = Argo.h; sourceTree = "<group>"; };
@@ -259,6 +265,7 @@
 				EAD9FAFF19D211630031E006 /* Comment.swift */,
 				EAD9FB0119D211C10031E006 /* Post.swift */,
 				EAD9FB1719D49A3E0031E006 /* TestModel.swift */,
+				F802D4C21A5EE061005E236C /* NSURL.swift */,
 			);
 			path = Models;
 			sourceTree = "<group>";
@@ -269,6 +276,7 @@
 				EAD9FB0F19D21AF50031E006 /* JSONFileReader.swift */,
 				EAD9FB0419D2143A0031E006 /* user_with_email.json */,
 				EAD9FB0819D214AA0031E006 /* user_without_email.json */,
+				F802D4C51A5EE2D5005E236C /* url.json */,
 				EAD9FB0919D214AA0031E006 /* TemplateIcon2x.png */,
 				EAD9FB1319D30ED00031E006 /* comment.json */,
 				EAD9FB1519D30F8D0031E006 /* post_no_comments.json */,
@@ -455,6 +463,7 @@
 				EA395DC41A52F8EB00EB607E /* array_root.json in Resources */,
 				F8E33FA51A51E0C20025A6E5 /* post_bad_comments.json in Resources */,
 				EAD9FB1419D30ED00031E006 /* comment.json in Resources */,
+				F802D4C61A5EE2D5005E236C /* url.json in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -480,6 +489,7 @@
 				EA395DC51A52F8EE00EB607E /* array_root.json in Resources */,
 				EA395DC21A5209C000EB607E /* post_bad_comments.json in Resources */,
 				F8EF75701A4CEC7100BDCC2D /* comment.json in Resources */,
+				F802D4C71A5EE2D5005E236C /* url.json in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -523,6 +533,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				EAD9FB1219D30E660031E006 /* EmbeddedJSONDecodingTests.swift in Sources */,
+				F802D4C31A5EE061005E236C /* NSURL.swift in Sources */,
 				EAD9FB1019D21AF50031E006 /* JSONFileReader.swift in Sources */,
 				EAD9FB0219D211C10031E006 /* Post.swift in Sources */,
 				EAD9FB1819D49A3E0031E006 /* TestModel.swift in Sources */,
@@ -555,6 +566,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				F8EF75731A4CEC7800BDCC2D /* Comment.swift in Sources */,
+				F802D4C41A5EE172005E236C /* NSURL.swift in Sources */,
 				F8EF75721A4CEC7800BDCC2D /* User.swift in Sources */,
 				F8EF756B1A4CEC6400BDCC2D /* EmbeddedJSONDecodingTests.swift in Sources */,
 				F8EF75751A4CEC7800BDCC2D /* TestModel.swift in Sources */,

diff --git a/Argo/Globals/JSONValue.swift b/Argo/Globals/JSONValue.swift
@@ -49,7 +49,7 @@ public enum JSONValue {
     return keys.reduce(self) { $0?[$1] }
   }
 
-  public static func map<A: JSONDecodable>(value: JSONValue) -> [A]? {
+  public static func map<A where A: JSONDecodable, A == A.DecodedType>(value: JSONValue) -> [A]? {
     switch value {
     case let .JSONArray(a):
       return a.reduce([]) { curry(+) <^> $0 <*> (pure <^> A.decode($1)) }

diff --git a/Argo/Operators/JSONOperators.swift b/Argo/Operators/JSONOperators.swift
@@ -1,7 +1,7 @@
 // MARK: Values
 
 // Pull embedded value from JSON
-public func <|<A: JSONDecodable>(json: JSONValue, keys: [String]) -> A? {
+public func <|<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, keys: [String]) -> A? {
   if let o = json.find(keys) {
     return A.decode(o)
   }
@@ -10,39 +10,39 @@ public func <|<A: JSONDecodable>(json: JSONValue, keys: [String]) -> A? {
 }
 
 // Pull value from JSON
-public func <|<A: JSONDecodable>(json: JSONValue, key: String) -> A? {
+public func <|<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, key: String) -> A? {
   return json <| [key]
 }
 
 // Pull embedded optional value from JSON
-public func <|?<A: JSONDecodable>(json: JSONValue, keys: [String]) -> A?? {
+public func <|?<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, keys: [String]) -> A?? {
   return pure(json <| keys)
 }
 
 // Pull optional value from JSON
-public func <|?<A: JSONDecodable>(json: JSONValue, key: String) -> A?? {
+public func <|?<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, key: String) -> A?? {
   return json <|? [key]
 }
 
 // MARK: Arrays
 
 // Pull embedded array from JSON
-public func <||<A: JSONDecodable>(json: JSONValue, keys: [String]) -> [A]? {
+public func <||<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, keys: [String]) -> [A]? {
   return json.find(keys) >>- JSONValue.map
 }
 
 // Pull array from JSON
-public func <||<A: JSONDecodable>(json: JSONValue, key: String) -> [A]? {
+public func <||<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, key: String) -> [A]? {
   return json <|| [key]
 }
 
 
 // Pull embedded optional array from JSON
-public func <||?<A: JSONDecodable>(json: JSONValue, keys: [String]) -> [A]?? {
+public func <||?<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, keys: [String]) -> [A]?? {
   return pure(json <|| keys)
 }
 
 // Pull optional array from JSON
-public func <||?<A: JSONDecodable>(json: JSONValue, key: String) -> [A]?? {
+public func <||?<A where A: JSONDecodable, A == A.DecodedType>(json: JSONValue, key: String) -> [A]?? {
   return json <||? [key]
 }
diff --git a/Argo/Protocols/JSONDecodable.swift b/Argo/Protocols/JSONDecodable.swift
@@ -1,3 +1,4 @@
 public protocol JSONDecodable {
-  class func decode(JSONValue) -> Self?
+  typealias DecodedType = Self
+  class func decode(JSONValue) -> DecodedType?
 }
diff --git a/ArgoTests/JSON/url.json b/ArgoTests/JSON/url.json
@@ -0,0 +1,3 @@
+{
+  "url": "http://example.com",
+}
diff --git a/ArgoTests/Models/NSURL.swift b/ArgoTests/Models/NSURL.swift
@@ -0,0 +1,13 @@
+import Argo
+import Foundation
+
+extension NSURL: JSONDecodable {
+  public typealias DecodedType = NSURL
+
+  public class func decode(j: JSONValue) -> DecodedType? {
+        switch j {
+        case .JSONString(let url): return NSURL(string: url)
+        default: return .None
+        }
+    }
+}
diff --git a/ArgoTests/Tests/ExampleTests.swift b/ArgoTests/Tests/ExampleTests.swift
@@ -20,4 +20,12 @@ class ExampleTests: XCTestCase {
     XCTAssert(user?.email != nil)
     XCTAssert(user?.email! == "[email protected]")
   }
+
+  func testDecodingNonFinalClass() {
+    let json: AnyObject? = JSONFileReader.JSON(fromFile: "url")
+    let url: NSURL? = json >>- JSONValue.parse >>- { $0["url"] >>- NSURL.decode }
+
+    XCTAssert(url != nil)
+    XCTAssert(url?.absoluteString == "http://example.com")
+  }
 }