Added an is_pair template for telling if a type is a std::pair object.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404162

dlib/is_kind.h

@@ -72,6 +72,19 @@ namespace dlib
         !*/
     };
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    struct is_pair : public default_is_kind_value  
+    {
+        /*!
+            - if (T is a std::pair object) then
+                - is_std_vector<T>::value == true
+            - else
+                - is_std_vector<T>::value == false
+        !*/
+    };
+
 // ----------------------------------------------------------------------------------------
 
     template <typename T>
@@ -97,6 +110,11 @@ namespace dlib
     template <typename T> struct is_std_vector<const T&>{ const static bool value = is_std_vector<T>::value; };
     template <typename T> struct is_std_vector<const T> { const static bool value = is_std_vector<T>::value; };
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T, typename U>
+    struct is_pair<std::pair<T,U> > { const static bool value = true; };
+
 // ----------------------------------------------------------------------------------------
 
 }