Added static empty instances of ObjList and NamedList.

git-svn-id: http://yate.null.ro/svn/yate/trunk@2280 acf43c95-373e-0410-b603-e72c3f656dc1

engine/NamedList.cpp

@@ -24,6 +24,13 @@
 
 using namespace TelEngine;
 
+static const NamedList s_empty("");
+
+const NamedList& NamedList::empty()
+{
+    return s_empty;
+}
+
 NamedList::NamedList(const char* name)
     : String(name)
 {

engine/ObjList.cpp

@@ -24,6 +24,13 @@
 
 using namespace TelEngine;
 
+static const ObjList s_empty;
+
+const ObjList& ObjList::empty()
+{
+    return s_empty;
+}
+
 ObjList::ObjList()
     : m_next(0), m_obj(0), m_delete(true)
 {

engine/String.cpp

@@ -182,7 +182,7 @@ void StringMatchPrivate::fixup()
 }
 
 
-static String s_empty;
+static const String s_empty;
 
 const String& String::empty()
 {

yateclass.h

@@ -1113,6 +1113,12 @@ public:
     inline void setDelete(bool autodelete)
 	{ m_delete = autodelete; }
 
+    /**
+     * A static empty object list
+     * @return Reference to a static empty list
+     */
+    static const ObjList& empty();
+
 private:
     ObjList* m_next;
     GenObject* m_obj;
@@ -1292,6 +1298,7 @@ public:
 
     /**
      * A static null String
+     * @return Reference to a static empty String
      */
     static const String& empty();
 
@@ -3180,6 +3187,12 @@ public:
      */
     int replaceParams(String& str, bool sqlEsc = false, char extraEsc = 0) const;
 
+    /**
+     * A static empty named list
+     * @return Reference to a static empty named list
+     */
+    static const NamedList& empty();
+
 private:
     NamedList(); // no default constructor please
     NamedList& operator=(const NamedList& value); // no assignment please