Clean up coding logic, reducing hard to maintain code duplication; improve box naming

Sources/XMLCoder/Auxiliaries/XMLElement.swift

@@ -23,24 +23,24 @@ internal class _XMLElement {
         self.children = children
     }
 
-    static func createRootElement(rootKey: String, object: ArrayBox) -> _XMLElement? {
+    static func createRootElement(rootKey: String, object: UnkeyedBox) -> _XMLElement? {
         let element = _XMLElement(key: rootKey)
 
         _XMLElement.createElement(parentElement: element, key: rootKey, object: object)
 
         return element
     }
 
-    static func createRootElement(rootKey: String, object: DictionaryBox) -> _XMLElement? {
+    static func createRootElement(rootKey: String, object: KeyedBox) -> _XMLElement? {
         let element = _XMLElement(key: rootKey)
 
         _XMLElement.modifyElement(element: element, parentElement: nil, key: nil, object: object)
 
         return element
     }
 
-    fileprivate static func modifyElement(element: _XMLElement, parentElement: _XMLElement?, key: String?, object: DictionaryBox) {
-        let attributesBox = object[_XMLElement.attributesKey] as? DictionaryBox
+    fileprivate static func modifyElement(element: _XMLElement, parentElement: _XMLElement?, key: String?, object: KeyedBox) {
+        let attributesBox = object[_XMLElement.attributesKey] as? KeyedBox
         let uniqueAttributes: [(String, String)]? = attributesBox?.unbox().compactMap { key, box in
             return box.xmlString().map { (key, $0) }
         }
@@ -59,11 +59,11 @@ internal class _XMLElement {
 
     fileprivate static func createElement(parentElement: _XMLElement, key: String, object: Box) {
         switch object {
-        case let box as ArrayBox:
+        case let box as UnkeyedBox:
             for box in box.unbox() {
                 _XMLElement.createElement(parentElement: parentElement, key: key, object: box)
             }
-        case let box as DictionaryBox:
+        case let box as KeyedBox:
             modifyElement(element: _XMLElement(key: key), parentElement: parentElement, key: key, object: box)
         case _:
             let element = _XMLElement(key: key, value: object.xmlString())
@@ -84,28 +84,28 @@ internal class _XMLElement {
         for childElement in children {
             for child in childElement.value {
                 if let content = child.value {
-                    if let oldContent = node[childElement.key] as? ArrayBox {
+                    if let oldContent = node[childElement.key] as? UnkeyedBox {
                         oldContent.append(StringBox(content))
                         // FIXME: Box is a reference type, so this shouldn't be necessary:
                         node[childElement.key] = oldContent
                     } else if let oldContent = node[childElement.key] {
-                        node[childElement.key] = ArrayBox([oldContent, StringBox(content)])
+                        node[childElement.key] = UnkeyedBox([oldContent, StringBox(content)])
                     } else {
                         node[childElement.key] = StringBox(content)
                     }
                 } else if !child.children.isEmpty || !child.attributes.isEmpty {
                     let newValue = child.flatten()
 
                     if let existingValue = node[childElement.key] {
-                        if let array = existingValue as? ArrayBox {
-                            array.append(DictionaryBox(newValue))
+                        if let unkeyed = existingValue as? UnkeyedBox {
+                            unkeyed.append(KeyedBox(newValue))
                             // FIXME: Box is a reference type, so this shouldn't be necessary:
-                            node[childElement.key] = array
+                            node[childElement.key] = unkeyed
                         } else {
-                            node[childElement.key] = ArrayBox([existingValue, DictionaryBox(newValue)])
+                            node[childElement.key] = UnkeyedBox([existingValue, KeyedBox(newValue)])
                         }
                     } else {
-                        node[childElement.key] = DictionaryBox(newValue)
+                        node[childElement.key] = KeyedBox(newValue)
                     }
                 }
             }

Sources/XMLCoder/Box/BoolBox.swift

@@ -34,10 +34,6 @@ extension BoolBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     /// # Lexical representation
     /// Boolean has a lexical representation consisting of the following
     /// legal literals {`true`, `false`, `1`, `0`}.
@@ -53,6 +49,10 @@ extension BoolBox: Box {
     }
 }
 
+extension BoolBox: SimpleBox {
+
+}
+
 extension BoolBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/Box.swift

@@ -9,7 +9,10 @@ import Foundation
 
 protocol Box {
     var isNull: Bool { get }
-    var isFragment: Bool { get }
-
     func xmlString() -> String?
 }
+
+/// A box that only describes a single atomic value.
+protocol SimpleBox: Box {
+
+}

Sources/XMLCoder/Box/DataBox.swift

@@ -46,15 +46,15 @@ extension DataBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     func xmlString() -> String? {
         return self.xmlString(format: self.format)
     }
 }
 
+extension DataBox: SimpleBox {
+
+}
+
 extension DataBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/DateBox.swift

@@ -88,15 +88,15 @@ extension DateBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     func xmlString() -> String? {
         return self.xmlString(format: self.format)
     }
 }
 
+extension DateBox: SimpleBox {
+
+}
+
 extension DateBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/DecimalBox.swift

@@ -33,10 +33,6 @@ extension DecimalBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     /// # Lexical representation
     /// Decimal has a lexical representation consisting of a finite-length sequence of
     /// decimal digits separated by a period as a decimal indicator.
@@ -60,6 +56,10 @@ extension DecimalBox: Box {
     }
 }
 
+extension DecimalBox: SimpleBox {
+
+}
+
 extension DecimalBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/FloatBox.swift

@@ -33,10 +33,6 @@ extension FloatBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     /// # Lexical representation
     /// float values have a lexical representation consisting of a mantissa followed, optionally,
     /// by the character `"E"` or `"e"`, followed by an exponent. The exponent **must** be an integer.
@@ -78,6 +74,10 @@ extension FloatBox: Box {
     }
 }
 
+extension FloatBox: SimpleBox {
+
+}
+
 extension FloatBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/IntBox.swift

@@ -33,10 +33,6 @@ extension IntBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     /// # Lexical representation
     /// Integer has a lexical representation consisting of a finite-length sequence of
     /// decimal digits with an optional leading sign. If the sign is omitted, `"+"` is assumed.
@@ -55,6 +51,10 @@ extension IntBox: Box {
     }
 }
 
+extension IntBox: SimpleBox {
+
+}
+
 extension IntBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/DictionaryBox.swift → Sources/XMLCoder/Box/KeyedBox.swift

@@ -1,5 +1,5 @@
 //
-//  DictionaryBox.swift
+//  KeyedBox.swift
 //  XMLCoderPackageDescription
 //
 //  Created by Vincent Esche on 11/19/18.
@@ -8,7 +8,7 @@
 import Foundation
 
 // Minimalist implementation of an order-preserving keyed box:
-class DictionaryBox {
+class KeyedBox {
     typealias Key = String
     typealias Value = Box
 
@@ -58,27 +58,30 @@ class DictionaryBox {
         return try self.unboxed.compactMap(transform)
     }
 
-    func mapValues(_ transform: (Value) throws -> Value) rethrows -> DictionaryBox {
-        return DictionaryBox(try self.unboxed.mapValues(transform))
+    func mapValues(_ transform: (Value) throws -> Value) rethrows -> KeyedBox {
+        return KeyedBox(try self.unboxed.mapValues(transform))
     }
 }
 
-extension DictionaryBox: Box {
+extension KeyedBox: Box {
     var isNull: Bool {
         return false
     }
 
-    var isFragment: Bool {
-        return false
-    }
-
     func xmlString() -> String? {
         return nil
     }
 }
 
+extension KeyedBox: Sequence {
+    typealias Iterator = Unboxed.Iterator
+
+    func makeIterator() -> Iterator {
+        return self.unboxed.makeIterator()
+    }
+}
 
-extension DictionaryBox: CustomStringConvertible {
+extension KeyedBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description
     }

Sources/XMLCoder/Box/NullBox.swift

@@ -16,15 +16,15 @@ extension NullBox: Box {
         return true
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     func xmlString() -> String? {
         return nil
     }
 }
 
+extension NullBox: SimpleBox {
+
+}
+
 extension NullBox: Equatable {
     static func == (lhs: NullBox, rhs: NullBox) -> Bool {
         return true

Sources/XMLCoder/Box/StringBox.swift

@@ -30,15 +30,15 @@ extension StringBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     func xmlString() -> String? {
         return self.unboxed.description
     }
 }
 
+extension StringBox: SimpleBox {
+
+}
+
 extension StringBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/UIntBox.swift

@@ -33,10 +33,6 @@ extension UIntBox: Box {
         return false
     }
 
-    var isFragment: Bool {
-        return true
-    }
-
     /// # Lexical representation
     /// Unsigned integer has a lexical representation consisting of an optional
     /// sign followed by a finite-length sequence of decimal digits.
@@ -58,6 +54,10 @@ extension UIntBox: Box {
     }
 }
 
+extension UIntBox: SimpleBox {
+
+}
+
 extension UIntBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description

Sources/XMLCoder/Box/ArrayBox.swift → Sources/XMLCoder/Box/UnkeyedBox.swift

@@ -1,5 +1,5 @@
 //
-//  ArrayBox.swift
+//  UnkeyedBox.swift
 //  XMLCoderPackageDescription
 //
 //  Created by Vincent Esche on 11/20/18.
@@ -8,7 +8,7 @@
 import Foundation
 
 // Minimalist implementation of an order-preserving unkeyed box:
-class ArrayBox {
+class UnkeyedBox {
     typealias Element = Box
     typealias Unboxed = [Element]
 
@@ -56,21 +56,25 @@ class ArrayBox {
     }
 }
 
-extension ArrayBox: Box {
+extension UnkeyedBox: Box {
     var isNull: Bool {
         return false
     }
 
-    var isFragment: Bool {
-        return false
-    }
-
     func xmlString() -> String? {
         return nil
     }
 }
 
-extension ArrayBox: CustomStringConvertible {
+extension UnkeyedBox: Sequence {
+    typealias Iterator = Unboxed.Iterator
+
+    func makeIterator() -> Iterator {
+        return self.unboxed.makeIterator()
+    }
+}
+
+extension UnkeyedBox: CustomStringConvertible {
     var description: String {
         return self.unboxed.description
     }

Sources/XMLCoder/Decoder/DecodingErrorExtension.swift

@@ -43,9 +43,9 @@ internal extension DecodingError {
             return "an unsigned integer value"
         case is FloatBox:
             return "a floating-point value"
-        case is ArrayBox:
+        case is UnkeyedBox:
             return "a array value"
-        case is DictionaryBox:
+        case is KeyedBox:
             return "a dictionary value"
         case _:
             return "\(type(of: box))"