Map: Add method value() to look up without creating entry

taglib/toolkit/tmap.h

@@ -153,6 +153,14 @@ namespace TagLib {
      */
     Map<Key, T> &erase(const Key &key);
 
+    /*!
+     * Returns the value associated with \a key.
+     *
+     * If the map does not contain \a key, it returns defaultValue.
+     * If no defaultValue is specified, it returns a default-constructed value.
+     */
+    const T value(const Key &key, const T &defaultValue = T()) const;
+
     /*!
      * Returns a reference to the value associated with \a key.
      *

taglib/toolkit/tmap.tcc

@@ -155,6 +155,13 @@ unsigned int Map<Key, T>::size() const
   return static_cast<unsigned int>(d->map.size());
 }
 
+template <class Key, class T>
+const T Map<Key, T>::value(const Key &key, const T &defaultValue) const
+{
+  ConstIterator it = d->map.find(key);
+  return it != d->map.end() ? it->second : defaultValue;
+}
+
 template <class Key, class T>
 const T &Map<Key, T>::operator[](const Key &key) const
 {

taglib/toolkit/tpropertymap.cpp

@@ -117,6 +117,12 @@ PropertyMap &PropertyMap::merge(const PropertyMap &other)
   return *this;
 }
 
+const StringList PropertyMap::value(const String &key,
+                                    const StringList &defaultValue) const
+{
+  return SimplePropertyMap::value(key.upper(), defaultValue);
+}
+
 const StringList &PropertyMap::operator[](const String &key) const
 {
   return SimplePropertyMap::operator[](key.upper());

taglib/toolkit/tpropertymap.h

@@ -191,6 +191,15 @@ namespace TagLib {
      */
     PropertyMap &merge(const PropertyMap &other);
 
+    /*!
+     * Returns the value associated with \a key.
+     *
+     * If the map does not contain \a key, it returns defaultValue.
+     * If no defaultValue is specified, it returns an empty string list.
+     */
+    const StringList value(const String &key,
+                           const StringList &defaultValue = StringList()) const;
+
     /*!
      * Returns a reference to the value associated with \a key.
      *