Improved error handling (fixed Issue tadija#62)

Added error property of ErrorType enum with possible error cases
Removed errorElementName static property
Modified subscript logic of AEXMLElement to return empty element with ElementNotFound error (if element does not exist)
Modified root property of AEXMLDocument to return empty element with RootElementMissing error (if root element does not exist)
Improved logic in testRootElement and testNotExistingElement unit tests
Minor changes in example ViewController and README.md

Example/ViewController.swift

@@ -92,8 +92,8 @@ class ViewController: UIViewController {
             // prints <cat breed="Siberian" color="lightgray">Tinna</cat>
             print(xmlDoc.root["cats"]["cat"].xmlStringCompact)
 
-            // prints element <badexample> not found
-            print(xmlDoc["badexample"]["notexisting"].stringValue)
+            // prints Optional(AEXMLExample.AEXMLElement.Error.ElementNotFound)
+            print(xmlDoc["NotExistingElement"].error)
         }
         catch {
             print("\(error)")

README.md

@@ -126,9 +126,9 @@ do {
     // prints <cat breed="Siberian" color="lightgray">Tinna</cat>
     print(xmlDoc.root["cats"]["cat"].xmlStringCompact)
 
-    // prints element <badexample> not found
-    print(xmlDoc["badexample"]["notexisting"].stringValue)
-    }
+    // prints Optional(AEXMLExample.AEXMLElement.Error.ElementNotFound)
+    print(xmlDoc["NotExistingElement"].error)
+}
 catch {
     print("\(error)")
 }

Source/AEXML.swift

@@ -32,6 +32,17 @@ import Foundation
 */
 public class AEXMLElement {
 
+    /// A type representing an error value that can be inside `error` property.
+    public enum Error: ErrorType {
+        case ElementNotFound
+        case RootElementMissing
+    }
+
+    private struct Defaults {
+        static let name = String()
+        static let attributes = [String : String]()
+    }
+
     // MARK: Properties
 
     /// Every `AEXMLElement` should have its parent element instead of `AEXMLDocument` which parent is `nil`.
@@ -49,6 +60,9 @@ public class AEXMLElement {
     /// XML Element attributes (defaults to empty dictionary).
     public var attributes: [String : String]
 
+    /// Error value (`nil` if there is no error).
+    public var error: Error?
+
     /// String representation of `value` property (if `value` is `nil` this is empty String).
     public var stringValue: String { return value ?? String() }
 
@@ -61,11 +75,6 @@ public class AEXMLElement {
     /// Double representation of `value` property (this is **0.00** if `value` can't be represented as Double).
     public var doubleValue: Double { return (stringValue as NSString).doubleValue }
 
-    private struct Defaults {
-        static let name = String()
-        static let attributes = [String : String]()
-    }
-
     // MARK: Lifecycle
 
     /**
@@ -85,18 +94,16 @@ public class AEXMLElement {
 
     // MARK: XML Read
 
-    /// This element name is used when unable to find element.
-    public static let errorElementName = "AEXMLError"
-
-    // The first element with given name **(AEXMLError element if not exists)**.
+    // The first element with given name **(Empty element with error if not exists)**.
     public subscript(key: String) -> AEXMLElement {
-        if name == AEXMLElement.errorElementName {
-            return self
-        } else {
-            let filtered = children.filter { $0.name == key }
-            let errorElement = AEXMLElement(AEXMLElement.errorElementName, value: "element <\(key)> not found")
-            return filtered.count > 0 ? filtered.first! : errorElement
+        guard let
+            first = children.filter({ $0.name == key }).first
+        else {
+            let errorElement = AEXMLElement(key)
+            errorElement.error = Error.ElementNotFound
+            return errorElement
         }
+        return first
     }
 
     /// Returns all of the elements with equal name as `self` **(nil if not exists)**.
@@ -323,9 +330,15 @@ public class AEXMLDocument: AEXMLElement {
     /// Options for NSXMLParser (default values are `false`)
     public let xmlParserOptions: NSXMLParserOptions
 
-    /// Root (the first child element) element of XML Document **(AEXMLError element if not exists)**.
-    private let errorElement = AEXMLElement(AEXMLElement.errorElementName, value: "XML Document must have root element.")
-    public var root: AEXMLElement { return children.count == 1 ? children.first! : errorElement }
+    /// Root (the first child element) element of XML Document **(Empty element with error if not exists)**.
+    public var root: AEXMLElement {
+        guard let rootElement = children.first else {
+            let errorElement = AEXMLElement()
+            errorElement.error = Error.RootElementMissing
+            return errorElement
+        }
+        return rootElement
+    }
 
     // MARK: Lifecycle
 

Tests/AEXMLTests.swift

@@ -81,6 +81,10 @@ class AEXMLTests: XCTestCase {
 
     func testRootElement() {
         XCTAssertEqual(exampleXML.root.name, "animals", "Should be able to find root element.")
+
+        let documentWithoutRootElement = AEXMLDocument()
+        let rootElement = documentWithoutRootElement.root
+        XCTAssertEqual(rootElement.error, AEXMLElement.Error.RootElementMissing, "Should have RootElementMissing error.")
     }
 
     func testParentElement() {
@@ -162,8 +166,9 @@ class AEXMLTests: XCTestCase {
 
     func testNotExistingElement() {
         // non-optional
-        XCTAssertEqual(exampleXML.root["ducks"]["duck"].name, AEXMLElement.errorElementName, "Should be able to tell you if element does not exist.")
-        XCTAssertEqual(exampleXML.root["ducks"]["duck"].stringValue, "element <ducks> not found", "Should be able to tell you which element does not exist.")
+        XCTAssertNotNil(exampleXML.root["ducks"]["duck"].error, "Should contain error inside element which does not exist.")
+        XCTAssertEqual(exampleXML.root["ducks"]["duck"].error, AEXMLElement.Error.ElementNotFound, "Should have ElementNotFound error.")
+        XCTAssertEqual(exampleXML.root["ducks"]["duck"].stringValue, String(), "Should have empty value.")
 
         // optional
         if let _ = exampleXML.root["ducks"]["duck"].first {