test const 0 capacity variants

Author: wusatosi

include/beman/inplace_vector/inplace_vector.hpp

@@ -45,10 +45,13 @@ using inplace_vector_internal_size_type =
 
 // array based storage is used so that we can satisfy constexpr requirement
 //
-// Selecting this storage type implies: std::is_trivial_v<T>
+// Selecting this storage type implies: std::is_trivial_v<T> or Capacity = 0
 template <typename T, std::size_t Capacity>
 struct inplace_vector_array_based_storage {
-  std::array<T, Capacity> elems;
+  using array_type = If<!std::is_const_v<T>, std::array<T, Capacity>,
+                        const std::array<std::remove_const_t<T>, Capacity>>;
+
+  array_type elems{};
 
   constexpr T *begin() { return elems.data(); }
   constexpr const T *begin() const { return elems.data(); }
@@ -57,7 +60,7 @@ struct inplace_vector_array_based_storage {
 // byte array based storage is used for non-constexpr environment, where default
 // initialization may not be available.
 //
-// Selecting this storage type implies: !std::is_trivial_v<T>
+// Selecting this storage type implies: !std::is_trivial_v<T> and Capacity != 0
 template <typename T, std::size_t Capacity>
 struct inplace_vector_bytes_based_storage {
   alignas(T) unsigned char elems[Capacity * sizeof(T)];
@@ -74,7 +77,7 @@ struct inplace_vector_destruct_base {
   using size_type = std::size_t;
   using internal_size_type = inplace_vector_internal_size_type<Capacity>;
   using internal_storage_type =
-      std::conditional_t<std::is_trivial_v<T>,
+      std::conditional_t<std::is_trivial_v<T> or Capacity == 0,
                          inplace_vector_array_based_storage<T, Capacity>,
                          inplace_vector_bytes_based_storage<T, Capacity>>;
 

src/beman/inplace_vector/tests/constexpr.test.cpp

@@ -16,51 +16,55 @@ struct NonTrivial {
 };
 static_assert(!std::is_trivial_v<NonTrivial>);
 
-static_assert(std::invoke([]() {
-                inplace_vector<int, 0> vec;
+template <typename T> constexpr bool test_empty_vec(T &vec) {
 
-                // sizes
-                S_ASSERT(vec.max_size() == 0);
-                S_ASSERT(vec.capacity() == 0);
-                S_ASSERT(vec.size() == 0);
-                S_ASSERT(vec.empty());
+  // sizes
+  S_ASSERT(vec.max_size() == 0);
+  S_ASSERT(vec.capacity() == 0);
+  S_ASSERT(vec.size() == 0);
+  S_ASSERT(vec.empty());
 
-                // itr
-                S_ASSERT(vec.begin() == vec.end());
-                S_ASSERT(vec.cbegin() == vec.cend());
-                S_ASSERT(vec.rbegin() == vec.rend());
-                S_ASSERT(vec.crbegin() == vec.crend());
+  // itr
+  S_ASSERT(vec.begin() == vec.end());
+  S_ASSERT(vec.cbegin() == vec.cend());
+  S_ASSERT(vec.rbegin() == vec.rend());
+  S_ASSERT(vec.crbegin() == vec.crend());
 
-                // push_back
-                S_ASSERT(vec.try_push_back(0) == nullptr);
-                S_ASSERT(vec.try_emplace_back(0) == nullptr);
+  // push_back
+  S_ASSERT(vec.try_push_back({}) == nullptr);
+  S_ASSERT(vec.try_emplace_back() == nullptr);
+
+  return true;
+}
 
+static_assert(std::invoke([]() {
+                inplace_vector<int, 0> vec;
+                test_empty_vec(vec);
                 return true;
               }),
               "0 capacity Trivial type");
 
 static_assert(std::invoke([]() {
-                inplace_vector<NonTrivial, 0> vec;
-
-                // sizes
-                S_ASSERT(vec.max_size() == 0);
-                S_ASSERT(vec.capacity() == 0);
-                S_ASSERT(vec.size() == 0);
-                S_ASSERT(vec.empty());
-
-                // itr
-                S_ASSERT(vec.begin() == vec.end());
-                S_ASSERT(vec.cbegin() == vec.cend());
-                S_ASSERT(vec.rbegin() == vec.rend());
-                S_ASSERT(vec.crbegin() == vec.crend());
-
-                // push_back
-                S_ASSERT(vec.try_push_back({}) == nullptr);
+                inplace_vector<const int, 0> vec;
+                test_empty_vec(vec);
+                return true;
+              }),
+              "0 capacity Trivial const type");
 
+static_assert(std::invoke([]() {
+                inplace_vector<NonTrivial, 0> vec;
+                test_empty_vec(vec);
                 return true;
               }),
               "0 capacity Non-trivial type");
 
+static_assert(std::invoke([]() {
+                inplace_vector<const NonTrivial, 0> vec;
+                test_empty_vec(vec);
+                return true;
+              }),
+              "0 capacity Non-trivial const type");
+
 static_assert(std::invoke([]() {
                 // sizes
                 {