c_array

Summary: [Folly] `c_array`, a container for returning C arrays from `constexpr` functions. May be used until C++17 may be assumed, since C++17 specifies `constexpr` member functions of `std::array` which make `std::array` suitable for the purpose and a better choice since it  can house zero-sized arrays.

Reviewed By: markisaa

Differential Revision: D21382680

fbshipit-source-id: 56a6528bb05988c1f1c8916f9267575783dc6276

folly/lang/CArray.h

+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+namespace folly {
+
+//  c_array
+//
+//  A container for C arrays. Suitable for returning non-zero-sized C arrays
+//  from constexpr functions.
+//
+//  Prefer std::array when using C++17 or later.
+template <typename V, size_t N>
+struct c_array {
+  V data[N];
+};
+
+} // namespace folly

folly/lang/Pretty.h

@@ -20,15 +20,14 @@
 #include <type_traits>
 
 #include <folly/Portability.h>
+#include <folly/lang/CArray.h>
 
 namespace folly {
 
 namespace detail {
 
 template <std::size_t S>
-struct pretty_carray {
-  char data[S];
-};
+using pretty_carray = c_array<char, S>;
 
 template <std::size_t S>
 static constexpr pretty_carray<S> pretty_carray_from(char const (&in)[S]) {