Change the default shape and strides of idx_map

c++/nda/layout/idx_map.hpp

@@ -105,10 +105,10 @@ namespace nda {
     static_assert((StrideOrder != 0) or (Rank == 1), "Error in nda::idx_map: StrideOrder can only be zero for 1D arrays");
 
     // Extents of all dimensions (the shape of the map).
-    std::array<long, Rank> len;
+    std::array<long, Rank> len{};
 
     // Strides of all dimensions.
-    std::array<long, Rank> str;
+    std::array<long, Rank> str{};
 
     public:
     /// Encoded static extents.
@@ -319,9 +319,6 @@ namespace nda {
       if constexpr (n_dynamic_extents == 0) {
         for (int u = 0; u < Rank; ++u) len[u] = static_extents[u];
         compute_strides_contiguous();
-      } else {
-        for (int u = 0; u < Rank; ++u)
-          len[u] = 0; // FIXME. Needed ? To have the proper invariant of the array : shape = (0,0,...) and pointer is null
       }
     }
 

test/c++/nda_layout_idx_map.cpp

@@ -33,6 +33,22 @@ std::array<long, sizeof...(Is)> make_array(Is... is) {
   return {is...};
 }
 
+TEST(NDA, IdxMapDefaultConstructed) {
+  // default constructed 3D index map in C-order
+  idx_map<3, 0, C_stride_order<3>, layout_prop_e::none> idxm{};
+  EXPECT_EQ(idxm.rank(), 3);
+  EXPECT_EQ(idxm.size(), 0);
+  EXPECT_EQ(idxm.ce_size(), 0);
+  EXPECT_EQ(idxm.lengths(), make_array(0, 0, 0));
+  EXPECT_EQ(idxm.strides(), make_array(0, 0, 0));
+  EXPECT_EQ(idxm.stride_order, (std::array<int, 3>{0, 1, 2}));
+  EXPECT_TRUE(idxm.is_contiguous());
+  EXPECT_TRUE(idxm.is_strided_1d());
+  EXPECT_TRUE(idxm.has_positive_strides());
+  EXPECT_TRUE(idxm.is_stride_order_C());
+  EXPECT_TRUE(idxm.is_stride_order_valid());
+}
+
 TEST(NDA, IdxMapContiguousCOrder) {
   // contiguous 2x3x4 index map in C-order
   idx_map<3, 0, C_stride_order<3>, layout_prop_e::contiguous> idxm{{2, 3, 4}};