Clarified the vector spec and added some more tests.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402739

dlib/geometry/vector_abstract.h

@@ -34,6 +34,14 @@ namespace dlib
                 this object is limited to representing points on the XY plane where
                 Z is set to 0.
 
+                Also note that this object performs the appropriate integer and 
+                floating point conversions and promotions when vectors of mixed
+                type are used together.  For example:
+                    vector<int,3> vi;
+                    vector<double,2> vd;
+                    vd + vi == a vector<double,3> object type since that is what
+                               is needed to contain the result of vi+vd without
+                               any loss of information.
         !*/
 
     public:
@@ -317,6 +325,37 @@ namespace dlib
 
     };
 
+// ----------------------------------------------------------------------------------------
+
+    template<typename T, typename U, long NR>
+    vector operator* (
+        const vector<T,NR> & lhs,
+        const U rhs
+    );
+    /*!
+        ensures
+            - returns the result of multiplying the scalar rhs by lhs
+    !*/
+    
+    template<typename T, typename U, long NR>
+    vector operator* (
+        const U lhs,
+        const vector<T,NR> & rhs   
+    );
+    /*! 
+        ensures
+            - returns the result of multiplying the scalar lhs by rhs
+    !*/
+
+    template<typename T, long NR>
+    inline void swap (
+        vector<T,NR> & a, 
+        vector<T,NR> & b 
+    ) { a.swap(b); }   
+    /*!
+        provides a global swap function
+    !*/
+
     template<typename T, long NR>
     inline void swap (
         vector<T,NR> & a, 

dlib/test/geometry.cpp

@@ -217,6 +217,27 @@ namespace
             (vd3/2).dot(vd2);
         }
 
+        {
+            dlib::vector<double,2> vd2;
+            dlib::vector<long,3> vl3;
+
+            vl3.x() = 1;
+            vl3.y() = 2;
+            vl3.z() = 3;
+
+            vd2.x() = 6.5;
+            vd2.y() = 7.5;
+
+            DLIB_CASSERT((vl3 + vd2).x() == 1+6.5,"");
+            DLIB_CASSERT((vl3 + vd2).y() == 2+7.5,"");
+            DLIB_CASSERT((vl3 + vd2).z() == 3+0,"");
+
+            DLIB_CASSERT((vl3 - vd2).x() == 1-6.5,"");
+            DLIB_CASSERT((vl3 - vd2).y() == 2-7.5,"");
+            DLIB_CASSERT((vl3 - vd2).z() == 3-0,"");
+
+        }
+
     }