Made directory implicitly convertible to string.

dlib/dir_nav/dir_nav_kernel_1.h

@@ -250,6 +250,9 @@ namespace dlib
         inline const std::string& full_name (
         ) const { return state.full_name; }
 
+        operator std::string (
+        ) const { return full_name(); }
+
         bool operator == (
             const directory& rhs
         ) const;

dlib/dir_nav/dir_nav_kernel_2.h

@@ -243,6 +243,9 @@ namespace dlib
         inline const std::string& full_name (
         ) const { return state.full_name; }
 
+        operator std::string (
+        ) const { return full_name(); }
+
         bool operator == (
             const directory& rhs
         ) const;

dlib/dir_nav/dir_nav_kernel_abstract.h

@@ -398,6 +398,14 @@ namespace dlib
                     - the last character of #full_name() is NOT get_separator()
         !*/
 
+        operator std::string (
+        ) const; 
+        /*!
+            ensures
+                - returns full_name()
+                  (i.e. provides an implicit conversion to string from dlib::directory)
+        !*/
+
         directory& operator= (
             const directory& rhs
         );