Made it so you can write statements like mymat = m = 0;

That is, chain the = operator when using a literal assignment on
matrix objects.

dlib/matrix/matrix.h

@@ -1592,7 +1592,7 @@ namespace dlib
             */
 
             literal_assign_helper(const literal_assign_helper& item) : m(item.m), r(item.r), c(item.c), has_been_used(false) {}
-            literal_assign_helper(matrix* m_): m(m_), r(0), c(0),has_been_used(false) {next();}
+            explicit literal_assign_helper(matrix* m_): m(m_), r(0), c(0),has_been_used(false) {next();}
             ~literal_assign_helper()
             {
                 DLIB_CASSERT(!has_been_used || r == m->nr(),
@@ -1620,6 +1620,8 @@ namespace dlib
 
         private:
 
+            friend class matrix;
+
             void next (
             ) const
             {
@@ -1639,6 +1641,14 @@ namespace dlib
 
     public:
 
+        matrix& operator = (
+            const literal_assign_helper& val
+        ) 
+        {  
+            *this = *val.m;
+            return *this;
+        }
+
         const literal_assign_helper operator = (
             const T& val
         ) 

dlib/test/matrix.cpp

@@ -1303,6 +1303,22 @@ namespace
             DLIB_TEST(is_finite(m));
         }
 
+        {
+            matrix<int> m(4,1), mm;
+
+            mm = (m = 1,2,3,4);
+            DLIB_TEST(m(0) == 1);
+            DLIB_TEST(m(1) == 2);
+            DLIB_TEST(m(2) == 3);
+            DLIB_TEST(m(3) == 4);
+            DLIB_TEST(mm == m);
+            DLIB_TEST(mm(0) == 1);
+            DLIB_TEST(mm(1) == 2);
+            DLIB_TEST(mm(2) == 3);
+            DLIB_TEST(mm(3) == 4);
+        }
+
+
     }