Fix decoding empty element as optional

Sources/XMLCoder/Auxiliaries/Box/BoolBox.swift

@@ -21,10 +21,6 @@ struct BoolBox: Equatable {
         case _: return nil
         }
     }
-
-    func unbox() -> Unboxed {
-        return unboxed
-    }
 }
 
 extension BoolBox: Box {

Sources/XMLCoder/Auxiliaries/Box/DataBox.swift

@@ -29,10 +29,6 @@ struct DataBox: Equatable {
         self.init(data, format: .base64)
     }
 
-    func unbox() -> Unboxed {
-        return unboxed
-    }
-
     func xmlString(format: Format) -> String {
         switch format {
         case .base64:

Sources/XMLCoder/Auxiliaries/Box/DateBox.swift

@@ -59,10 +59,6 @@ struct DateBox: Equatable {
         self.init(date, format: .formatter(formatter))
     }
 
-    func unbox() -> Unboxed {
-        return unboxed
-    }
-
     func xmlString(format: Format) -> String {
         switch format {
         case .secondsSince1970:

Sources/XMLCoder/Auxiliaries/Box/DecimalBox.swift

@@ -22,10 +22,6 @@ struct DecimalBox: Equatable {
         }
         self.init(unboxed)
     }
-
-    func unbox() -> Unboxed {
-        return unboxed
-    }
 }
 
 extension DecimalBox: Box {

Sources/XMLCoder/Auxiliaries/Box/KeyedBox.swift

@@ -16,7 +16,7 @@ struct KeyedBox {
     var elements = Elements()
     var attributes = Attributes()
 
-    func unbox() -> (elements: Elements, attributes: Attributes) {
+    var unboxed: (elements: Elements, attributes: Attributes) {
         return (
             elements: elements,
             attributes: attributes

Sources/XMLCoder/Auxiliaries/Box/SharedBox.swift

@@ -6,7 +6,7 @@
 //
 
 class SharedBox<Unboxed: Box> {
-    fileprivate var unboxed: Unboxed
+    private(set) var unboxed: Unboxed
 
     init(_ wrapped: Unboxed) {
         unboxed = wrapped

Sources/XMLCoder/Auxiliaries/Box/StringBox.swift

@@ -17,10 +17,6 @@ struct StringBox: Equatable {
     init(xmlString: Unboxed) {
         self.init(xmlString)
     }
-
-    func unbox() -> Unboxed {
-        return unboxed
-    }
 }
 
 extension StringBox: Box {

Sources/XMLCoder/Auxiliaries/Box/URLBox.swift

@@ -22,10 +22,6 @@ struct URLBox: Equatable {
         }
         self.init(unboxed)
     }
-
-    func unbox() -> Unboxed {
-        return unboxed
-    }
 }
 
 extension URLBox: Box {

Sources/XMLCoder/Auxiliaries/Box/UnkeyedBox.swift

@@ -29,10 +29,6 @@ struct UnkeyedBox {
         self.unboxed = unboxed
     }
 
-    func unbox() -> Unboxed {
-        return unboxed
-    }
-
     mutating func append(_ newElement: Element) {
         unboxed.append(newElement)
     }

Sources/XMLCoder/Auxiliaries/XMLCoderElement.swift

@@ -256,7 +256,7 @@ extension XMLCoderElement {
 
             switch box {
             case let sharedUnkeyedBox as SharedBox<UnkeyedBox>:
-                let box = sharedUnkeyedBox.unbox()
+                let box = sharedUnkeyedBox.unboxed
                 elements.append(contentsOf: box.map {
                     XMLCoderElement(key: key, box: $0)
                 })
@@ -266,7 +266,7 @@ extension XMLCoderElement {
                     XMLCoderElement(key: key, box: $0)
                 })
             case let sharedKeyedBox as SharedBox<KeyedBox>:
-                let box = sharedKeyedBox.unbox()
+                let box = sharedKeyedBox.unboxed
                 elements.append(XMLCoderElement(key: key, box: box))
             case let keyedBox as KeyedBox:
                 elements.append(XMLCoderElement(key: key, box: keyedBox))
@@ -297,9 +297,9 @@ extension XMLCoderElement {
     init(key: String, box: Box) {
         switch box {
         case let sharedUnkeyedBox as SharedBox<UnkeyedBox>:
-            self.init(key: key, box: sharedUnkeyedBox.unbox())
+            self.init(key: key, box: sharedUnkeyedBox.unboxed)
         case let sharedKeyedBox as SharedBox<KeyedBox>:
-            self.init(key: key, box: sharedKeyedBox.unbox())
+            self.init(key: key, box: sharedKeyedBox.unboxed)
         case let unkeyedBox as UnkeyedBox:
             self.init(key: key, box: unkeyedBox)
         case let keyedBox as KeyedBox:

Sources/XMLCoder/Decoder/XMLDecoderImplementation.swift

@@ -168,29 +168,29 @@ extension XMLDecoderImplementation {
 
     func unbox(_ box: Box) throws -> Bool {
         let stringBox: StringBox = try typedBox(box, for: Bool.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         guard let boolBox = BoolBox(xmlString: string) else {
             throw DecodingError._typeMismatch(at: codingPath, expectation: Bool.self, reality: box)
         }
 
-        return boolBox.unbox()
+        return boolBox.unboxed
     }
 
     func unbox(_ box: Box) throws -> Decimal {
         let stringBox: StringBox = try typedBox(box, for: Decimal.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         guard let decimalBox = DecimalBox(xmlString: string) else {
             throw DecodingError._typeMismatch(at: codingPath, expectation: Decimal.self, reality: box)
         }
 
-        return decimalBox.unbox()
+        return decimalBox.unboxed
     }
 
     func unbox<T: BinaryInteger & SignedInteger & Decodable>(_ box: Box) throws -> T {
         let stringBox: StringBox = try typedBox(box, for: T.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         guard let intBox = IntBox(xmlString: string) else {
             throw DecodingError._typeMismatch(at: codingPath, expectation: T.self, reality: box)
@@ -208,7 +208,7 @@ extension XMLDecoderImplementation {
 
     func unbox<T: BinaryInteger & UnsignedInteger & Decodable>(_ box: Box) throws -> T {
         let stringBox: StringBox = try typedBox(box, for: T.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         guard let uintBox = UIntBox(xmlString: string) else {
             throw DecodingError._typeMismatch(at: codingPath, expectation: T.self, reality: box)
@@ -226,7 +226,7 @@ extension XMLDecoderImplementation {
 
     func unbox<T: BinaryFloatingPoint & Decodable>(_ box: Box) throws -> T {
         let stringBox: StringBox = try typedBox(box, for: T.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         guard let floatBox = FloatBox(xmlString: string) else {
             throw DecodingError._typeMismatch(at: codingPath, expectation: T.self, reality: box)
@@ -244,7 +244,7 @@ extension XMLDecoderImplementation {
 
     func unbox(_ box: Box) throws -> String {
         let stringBox: StringBox = try typedBox(box, for: String.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         return string
     }
@@ -258,48 +258,48 @@ extension XMLDecoderImplementation {
 
         case .secondsSince1970:
             let stringBox: StringBox = try typedBox(box, for: Date.self)
-            let string = stringBox.unbox()
+            let string = stringBox.unboxed
 
             guard let dateBox = DateBox(secondsSince1970: string) else {
                 throw DecodingError.dataCorrupted(DecodingError.Context(
                     codingPath: codingPath,
                     debugDescription: "Expected date string to be formatted in seconds since 1970."
                 ))
             }
-            return dateBox.unbox()
+            return dateBox.unboxed
         case .millisecondsSince1970:
             let stringBox: StringBox = try typedBox(box, for: Date.self)
-            let string = stringBox.unbox()
+            let string = stringBox.unboxed
 
             guard let dateBox = DateBox(millisecondsSince1970: string) else {
                 throw DecodingError.dataCorrupted(DecodingError.Context(
                     codingPath: codingPath,
                     debugDescription: "Expected date string to be formatted in milliseconds since 1970."
                 ))
             }
-            return dateBox.unbox()
+            return dateBox.unboxed
         case .iso8601:
             let stringBox: StringBox = try typedBox(box, for: Date.self)
-            let string = stringBox.unbox()
+            let string = stringBox.unboxed
 
             guard let dateBox = DateBox(iso8601: string) else {
                 throw DecodingError.dataCorrupted(DecodingError.Context(
                     codingPath: codingPath,
                     debugDescription: "Expected date string to be ISO8601-formatted."
                 ))
             }
-            return dateBox.unbox()
+            return dateBox.unboxed
         case let .formatted(formatter):
             let stringBox: StringBox = try typedBox(box, for: Date.self)
-            let string = stringBox.unbox()
+            let string = stringBox.unboxed
 
             guard let dateBox = DateBox(xmlString: string, formatter: formatter) else {
                 throw DecodingError.dataCorrupted(DecodingError.Context(
                     codingPath: codingPath,
                     debugDescription: "Date string does not match format expected by formatter."
                 ))
             }
-            return dateBox.unbox()
+            return dateBox.unboxed
         case let .custom(closure):
             storage.push(container: box)
             defer { storage.popContainer() }
@@ -315,15 +315,15 @@ extension XMLDecoderImplementation {
             return try Data(from: self)
         case .base64:
             let stringBox: StringBox = try typedBox(box, for: Data.self)
-            let string = stringBox.unbox()
+            let string = stringBox.unboxed
 
             guard let dataBox = DataBox(base64: string) else {
                 throw DecodingError.dataCorrupted(DecodingError.Context(
                     codingPath: codingPath,
                     debugDescription: "Encountered Data is not valid Base64"
                 ))
             }
-            return dataBox.unbox()
+            return dataBox.unboxed
         case let .custom(closure):
             storage.push(container: box)
             defer { storage.popContainer() }
@@ -333,7 +333,7 @@ extension XMLDecoderImplementation {
 
     func unbox(_ box: Box) throws -> URL {
         let stringBox: StringBox = try typedBox(box, for: URL.self)
-        let string = stringBox.unbox()
+        let string = stringBox.unboxed
 
         guard let urlBox = URLBox(xmlString: string) else {
             throw DecodingError.dataCorrupted(DecodingError.Context(
@@ -342,7 +342,7 @@ extension XMLDecoderImplementation {
             ))
         }
 
-        return urlBox.unbox()
+        return urlBox.unboxed
     }
 
     private struct TypeMismatch: Error {}
@@ -369,8 +369,19 @@ extension XMLDecoderImplementation {
             decoded = value
         } else {
             storage.push(container: box)
-            decoded = try type.init(from: self)
-            storage.popContainer()
+            defer { storage.popContainer() }
+
+            do {
+                decoded = try type.init(from: self)
+            } catch {
+                guard case DecodingError.valueNotFound = error,
+                    let type = type as? AnyOptional.Type,
+                    let result = type.init() as? T else {
+                    throw error
+                }
+
+                return result
+            }
         }
 
         guard let result = decoded else {

Tests/XMLCoderTests/Box/BoolBoxTests.swift

@@ -24,7 +24,7 @@ class BoolBoxTests: XCTestCase {
 
         for unboxed in values {
             let box = Boxed(unboxed)
-            XCTAssertEqual(box.unbox(), unboxed)
+            XCTAssertEqual(box.unboxed, unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/DataBoxTests.swift

@@ -24,7 +24,7 @@ class DataBoxTests: XCTestCase {
 
         for unboxed in values {
             let box = Boxed(unboxed, format: .base64)
-            XCTAssertEqual(box.unbox(), unboxed)
+            XCTAssertEqual(box.unboxed, unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/DateBoxTests.swift

@@ -31,7 +31,7 @@ class DateBoxTests: XCTestCase {
 
         for unboxed in values {
             let box = Boxed(unboxed, format: .iso8601)
-            XCTAssertEqual(box.unbox(), unboxed)
+            XCTAssertEqual(box.unboxed, unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/DecimalBoxTests.swift

@@ -26,7 +26,7 @@ class DecimalBoxTests: XCTestCase {
 
         for unboxed in values {
             let box = Boxed(unboxed)
-            XCTAssertEqual(box.unbox(), unboxed)
+            XCTAssertEqual(box.unboxed, unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/KeyedBoxTests.swift

@@ -22,7 +22,7 @@ class KeyedBoxTests: XCTestCase {
     }
 
     func testUnbox() {
-        let (elements, attributes) = box.unbox()
+        let (elements, attributes) = box.unboxed
 
         XCTAssertEqual(elements.count, 2)
         XCTAssertEqual(elements["foo"] as? StringBox, StringBox("bar"))

Tests/XMLCoderTests/Box/SharedBoxTests.swift

@@ -12,7 +12,7 @@ class SharedBoxTests: XCTestCase {
     func testInit() {
         let box = SharedBox(BoolBox(false))
         box.withShared { shared in
-            XCTAssertFalse(shared.unbox())
+            XCTAssertFalse(shared.unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/StringBoxTests.swift

@@ -27,7 +27,7 @@ class StringBoxTests: XCTestCase {
 
         for unboxed in values {
             let box = Boxed(unboxed)
-            XCTAssertEqual(box.unbox(), unboxed)
+            XCTAssertEqual(box.unboxed, unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/URLBoxTests.swift

@@ -24,7 +24,7 @@ class URLBoxTests: XCTestCase {
 
         for unboxed in values {
             let box = Boxed(unboxed)
-            XCTAssertEqual(box.unbox(), unboxed)
+            XCTAssertEqual(box.unboxed, unboxed)
         }
     }
 

Tests/XMLCoderTests/Box/UnkeyedBoxTests.swift

@@ -19,7 +19,7 @@ class UnkeyedBoxTests: XCTestCase {
     }
 
     func testUnbox() {
-        let unboxed = box.unbox()
+        let unboxed = box.unboxed
         XCTAssertEqual(unboxed.count, 2)
         XCTAssertEqual(unboxed[0] as? StringBox, StringBox("foo"))
         XCTAssertEqual(unboxed[1] as? IntBox, IntBox(42))