Issue #41 - Bring method of determining IE version up to date

src/shared/Registry.h

+#ifndef REGISTRY_H
+#define REGISTRY_H
+
 #include <string>
 #include <Windows.h>
 
 namespace AdblockPlus
 {
   /**
    * An open key in the system registry.
+   *
+   * This class is not completely general.
+   * In particular, it cannot encapsulate the predefined registry keys
+   *   such as HKEY_CLASSES_ROOT.
+   * These classes are considered "always open",
+   *   and the destructor should not close them.
+   * Rather than trying to detect these predefined keys,
+   *   we simply don't allow them to be constructed.
+   * In practice, this is a limitation without much consequence.
+   * If this were a library designed for standalone use,
+   *   this limitation might not be appropriate, but it's fine here.
    */
-  class Registry_Key
+  class RegistryKey
   {
     /**
-     * Handle to an open registry key.
+     * Handle to registry key that is open and not predefined.
      */
     HKEY key;
 
-    /**
-     * Flag whether the registry key is predefined or not.
-     *
-     * Predefined key values are considered "always open" and should not be closed in the destructor.
-     */
-    bool is_predefined;
-
   public:
     /**
-     * Enumeration for predefined root keys.
+     * Constructor to open a key as a subkey key of an existing parent.
+     * Opens the key with read-only access.
+     *
+     * The constructor throws if 'key_name' is not found,
+     *   to preserve the invariant that the registry key is open.
+     * The constructor also throws if 'key_name' is empty,
+     *   to preserve the invariant the the registry key is not predefinded.
+     *
+     * \param parent
+     *   An open registry key. This may be one of the predefined keys.
+     * \param key_name
+     *   Name of the subkey to be opened under the parent.
      */
-    enum class Predefined
-      : unsigned int
-    {
-      HKCR = 0,   // HKEY_CLASSES_ROOT
-      HKCC,       // HKEY_CURRENT_CONFIG
-      HKCU,       // HKEY_CURRENT_USER
-      HKLM,       // HKEY_LOCAL_MACHINE
-      HKU         // HKEY_USERS
-    };
+    RegistryKey(HKEY parent, const std::wstring& key_name);
 
     /**
-     * Constructor to open a key under one of the predefined roots.
-     * Opens the key with read-only access.
-     *
-     * Because the invariant of this class is that the underlying registry key is open,
-     *   this constructor throws if 'key_name' is not found.
+     * Destructor always closes the key.
      */
-    Registry_Key(Predefined root, std::wstring key_name);
-
-    /**
-     * Constructor for one of the predefined roots.
-     */
-    Registry_Key(Predefined root);
-
-    /**
-     * Destructor closes the key if it's not a predefined one.
-     */
-    ~Registry_Key();
+    ~RegistryKey();
 
     /**
      * Retrieve a value from a name-value pair within the present key.
      *
      * Throws if the name is not found within the dictionary.
      * Throws if the name is found but is not a string.
      */
-    std::wstring value_wstring(std::wstring name) const;
+    std::wstring value_wstring(const std::wstring& name) const;
   };
 }
 
+#endif