fix flatten for rank 0 (#75)

Author: lgarithm

include/ttl/bits/std_tensor_reshape.hpp

@@ -9,7 +9,7 @@ namespace internal
 {
 template <typename R, typename S, typename D, typename A>
 struct flattener {
-    using S1 = typename S::template subshape_t<S::rank - 1>;
+    using S1 = basic_shape<1, typename S::dimension_type>;
     using vector =
         basic_tensor<R, S1, D, typename basic_tensor_traits<R, A, D>::Access>;
 

tests/test_tensor_reshape.cpp

@@ -16,3 +16,40 @@ TEST(tensor_reshape_test, test_chunk)
     static_assert(std::is_same<decltype(z), ttl::tensor_view<int, 1>>::value,
                   "");
 }
+
+template <typename R, ttl::rank_t r>
+void test_flatten(const ttl::tensor<R, r> &t)
+{
+    {
+        auto v = ttl::flatten(t);
+        static_assert(std::is_same<decltype(v), ttl::vector_ref<R>>::value, "");
+        ASSERT_EQ(v.shape().size(), t.shape().size());
+    }
+    {
+        auto v = ttl::flatten(ttl::ref(t));
+        static_assert(std::is_same<decltype(v), ttl::vector_ref<R>>::value, "");
+        ASSERT_EQ(v.shape().size(), t.shape().size());
+    }
+    {
+        auto v = ttl::flatten(ttl::view(t));
+        static_assert(std::is_same<decltype(v), ttl::vector_view<R>>::value,
+                      "");
+        ASSERT_EQ(v.shape().size(), t.shape().size());
+    }
+}
+
+TEST(tensor_reshape_test, test_flatten)
+{
+    {
+        ttl::tensor<int, 0> x;
+        test_flatten(x);
+    }
+    {
+        ttl::tensor<int, 1> x(4);
+        test_flatten(x);
+    }
+    {
+        ttl::tensor<int, 2> x(4, 5);
+        test_flatten(x);
+    }
+}