Improved the alias detection capability of kernel_matrix() expressions. Now statements

of the form: sample = kernel_matrix(kern, *, sample) can be used since the aliasing of
sample will be handled.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403862

dlib/svm/kernel_matrix.h

@@ -112,7 +112,7 @@ namespace dlib
     }
 
     template <typename K, typename vect_type1, typename vect_type2>
-    struct op_kern_mat : does_not_alias 
+    struct op_kern_mat  
     {
         op_kern_mat( 
             const K& kern_, 
@@ -149,6 +149,18 @@ namespace dlib
 
         long nr () const { return impl::size<K>(vect1); }
         long nc () const { return impl::size<K>(vect2); }
+
+        template <typename U> bool aliases               ( const matrix_exp<U>& item ) const { return alias_helper(item.ref()); }
+        template <typename U> bool destructively_aliases ( const matrix_exp<U>& item ) const { return alias_helper(item.ref()); }
+
+        template <typename U> bool alias_helper  ( const U& ) const { return false; }
+
+        typedef typename K::sample_type samp_type;
+
+        // Say we destructively alias if one of the vect* objects is actually item.
+        bool alias_helper                   (const samp_type& item ) const { return are_same(item, vect1) || are_same(item, vect2); }
+        template <typename U> bool are_same (const samp_type& a, const U& b)         const { return false; }
+        bool are_same                       (const samp_type& a, const samp_type& b) const { return (&a == &b); }
     }; 
 
 // ----------------------------------------------------------------------------------------

dlib/test/kernel_matrix.cpp

@@ -46,6 +46,7 @@ namespace
             std::vector<sample_type> vect2;
 
             const sample_type samp = randm(4,1);
+            sample_type samp2, samp3;
 
             vect1.push_back(randm(4,1));
             vect1.push_back(randm(4,1));
@@ -122,6 +123,17 @@ namespace
             DLIB_TEST(equal(K, kernel_matrix(kern, samp, vector_to_matrix(vect1))));
 
 
+
+            samp2 = samp;
+            samp3 = samp;
+
+            // test the alias detection
+            samp2 = kernel_matrix(kern, vect1, samp2);
+            DLIB_TEST(equal(samp2, kernel_matrix(kern, vect1, samp)));
+
+            samp3 = trans(kernel_matrix(kern, samp3, vect2));
+            DLIB_TEST(equal(samp3, trans(kernel_matrix(kern, samp, vect2))));
+
         }
     };