Support mutating JSON values

GenericJSON/Querying.swift

@@ -4,42 +4,87 @@ public extension JSON {
 
     /// Return the string value if this is a `.string`, otherwise `nil`
     var stringValue: String? {
-        if case .string(let value) = self {
-            return value
+        get {
+            if case .string(let value) = self {
+                return value
+            }
+            return nil
+        }
+        set {
+            if let newValue = newValue {
+                self = .string(newValue)
+            } else {
+                self = .null
+            }
         }
-        return nil
     }
 
     /// Return the double value if this is a `.number`, otherwise `nil`
     var doubleValue: Double? {
-        if case .number(let value) = self {
-            return value
+        get {
+            if case .number(let value) = self {
+                return value
+            }
+            return nil
+        }
+        set {
+            if let newValue = newValue {
+                self = .number(newValue)
+            } else {
+                self = .null
+            }
         }
-        return nil
     }
 
     /// Return the bool value if this is a `.bool`, otherwise `nil`
     var boolValue: Bool? {
-        if case .bool(let value) = self {
-            return value
+        get {
+            if case .bool(let value) = self {
+                return value
+            }
+            return nil
+        }
+        set {
+            if let newValue = newValue {
+                self = .bool(newValue)
+            } else {
+                self = .null
+            }
         }
-        return nil
     }
 
     /// Return the object value if this is an `.object`, otherwise `nil`
     var objectValue: [String: JSON]? {
-        if case .object(let value) = self {
-            return value
+        get {
+            if case .object(let value) = self {
+                return value
+            }
+            return nil
+        }
+        set {
+            if let newValue = newValue {
+                self = .object(newValue)
+            } else {
+                self = .null
+            }
         }
-        return nil
     }
 
     /// Return the array value if this is an `.array`, otherwise `nil`
     var arrayValue: [JSON]? {
-        if case .array(let value) = self {
-            return value
+        get {
+            if case .array(let value) = self {
+                return value
+            }
+            return nil
+        }
+        set {
+            if let newValue = newValue {
+                self = .array(newValue)
+            } else {
+                self = .null
+            }
         }
-        return nil
     }
 
     /// Return `true` iff this is `.null`
@@ -50,36 +95,62 @@ public extension JSON {
         return false
     }
 
+    mutating func setToNull() {
+        self = .null
+    }
+
     /// If this is an `.array`, return item at index
     ///
     /// If this is not an `.array` or the index is out of bounds, returns `nil`.
     subscript(index: Int) -> JSON? {
-        if case .array(let arr) = self, arr.indices.contains(index) {
-            return arr[index]
+        get {
+            if case .array(let arr) = self, arr.indices.contains(index) {
+                return arr[index]
+            }
+            return nil
+        }
+        set {
+            guard case .array(var arr) = self else {
+                fatalError("Subscript assignment of JSON value that is not an array")
+            }
+
+            arr[index] = newValue!
+            self = .array(arr)
         }
-        return nil
     }
 
     /// If this is an `.object`, return item at key
     subscript(key: String) -> JSON? {
-        if case .object(let dict) = self {
-            return dict[key]
+        get {
+            if case .object(let dict) = self {
+                return dict[key]
+            }
+            return nil
+        }
+        set {
+            guard case .object(var dict) = self else {
+                fatalError("Subscript assignment of JSON value that is not a dictionary")
+            }
+
+            dict[key] = newValue!
+            self = .object(dict)
         }
-        return nil
     }
 
     /// Dynamic member lookup sugar for string subscripts
     ///
     /// This lets you write `json.foo` instead of `json["foo"]`.
     subscript(dynamicMember member: String) -> JSON? {
-        return self[member]
+        get { self[member] }
+        set { self[member] = newValue }
     }
 
     /// Return the JSON type at the keypath if this is an `.object`, otherwise `nil`
     ///
     /// This lets you write `json[keyPath: "foo.bar.jar"]`.
     subscript(keyPath keyPath: String) -> JSON? {
-        return queryKeyPath(keyPath.components(separatedBy: "."))
+        get { queryKeyPath(keyPath.components(separatedBy: ".")) }
+        set { updateKeyPath(keyPath.components(separatedBy: "."), &self, newValue!) }
     }
 
     func queryKeyPath<T>(_ path: T) -> JSON? where T: Collection, T.Element == String {
@@ -103,5 +174,29 @@ public extension JSON {
 
         return tail.isEmpty ? value : value.queryKeyPath(tail)
     }
-
+
+    func updateKeyPath<T>(_ path: T, _ json: inout JSON, _ newValue: JSON) where T: Collection, T.Element == String {
+        // Only object values may be subscripted
+        guard case .object = json else {
+            fatalError("Keypath \(path) applied to non-object")
+        }
+
+        // Is the path non-empty?
+        guard let head = path.first else {
+            return
+        }
+
+        let tail = path.dropFirst()
+
+        guard !tail.isEmpty else {
+            json[head] = newValue
+            return
+        }
+
+        if json[head] == nil {
+            json[head] = [:]
+        }
+
+        updateKeyPath(tail, &json[head]!, newValue)
+    }
 }

GenericJSONTests/CodingTests.swift

@@ -22,13 +22,6 @@ class CodingTests: XCTestCase {
             """)
     }
 
-    func testFragmentEncoding() {
-        let fragments: [JSON] = ["foo", 1, true, nil]
-        for f in fragments {
-            XCTAssertThrowsError(try JSONEncoder().encode(f))
-        }
-    }
-
     func testDecoding() throws {
         let input = """
             {"array":[1],"num":1,"bool":true,"obj":{},"null":null,"str":"baz"}

GenericJSONTests/InitializationTests.swift

@@ -43,8 +43,8 @@ class InitializationTests: XCTestCase {
     func testInitializationFromCodable() throws {
 
         struct Foo: Codable {
-            let a: String = "foo"
-            let b: Bool = true
+            var a: String = "foo"
+            var b: Bool = true
         }
 
         let json = try JSON(encodable: Foo())