From 736ab7a5556a5e6ddf93adea91baf4516abe830a Mon Sep 17 00:00:00 2001
From: Laurent Rineau <laurent.rineau@cgal.org>
Date: Fri, 19 Apr 2024 16:47:38 +0200
Subject: [PATCH] make_array now use perfect forwarding, and remove
 fwd_make_array

---
 STL_Extension/include/CGAL/array.h            | 40 ++++++++++---------
 .../STL_Extension/test_fwd_make_array.cpp     |  5 ++-
 2 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/STL_Extension/include/CGAL/array.h b/STL_Extension/include/CGAL/array.h
index 7b15f064db87..98892c6257df 100644
--- a/STL_Extension/include/CGAL/array.h
+++ b/STL_Extension/include/CGAL/array.h
@@ -45,34 +45,36 @@ namespace CGAL {
 
 // It's also untrue that this is not documented...  It is !
 
-template< typename T, typename... Args >
-BOOST_CXX14_CONSTEXPR
-std::array< T, 1 + sizeof...(Args) >
-make_array(const T & t, const Args & ... args)
-{
-  std::array< T, 1 + sizeof...(Args) > a = { { t, static_cast<T>(args)... } };
-  return a;
-}
+template <typename T, typename ...Args>
+struct Make_array_element_type {
+  using type = T;
+};
 
-template< typename T, typename... Args >
-BOOST_CXX14_CONSTEXPR
-std::array< T, sizeof...(Args) >
-fwd_make_array(Args && ... args)
+template <typename ...Args>
+struct Make_array_element_type<void, Args...> {
+  using type = typename std::common_type_t<Args...>;
+};
+
+template <typename T, typename ...Args>
+using Make_array_element_type_t = typename Make_array_element_type<T, Args...>::type;
+
+template<typename T = void, typename... Args>
+constexpr
+std::array<Make_array_element_type_t<T, Args...>, sizeof...(Args) >
+make_array(Args&& ... args)
 {
-  std::array< T, sizeof...(Args) > a = { static_cast<T>(std::forward<Args>(args))... };
-  return a;
+  return {{ std::forward<Args>(args)... }};
 }
 
-
 // Functor version
 struct Construct_array
 {
-  template <typename T, typename... Args>
+  template <typename... Args>
   constexpr
-  std::array<T, 1 + sizeof...(Args)>
-  operator()(const T& t, const Args& ... args) const
+  decltype(auto)
+  operator()(Args&& ... args) const
   {
-    return make_array (t, args...);
+    return make_array( std::forward<Args>(args)... );
   }
 };
 
diff --git a/STL_Extension/test/STL_Extension/test_fwd_make_array.cpp b/STL_Extension/test/STL_Extension/test_fwd_make_array.cpp
index 305b09d3f1c1..6d55735a14f5 100644
--- a/STL_Extension/test/STL_Extension/test_fwd_make_array.cpp
+++ b/STL_Extension/test/STL_Extension/test_fwd_make_array.cpp
@@ -15,8 +15,9 @@ struct A // move-only class, move-constructible from B
 int main()
 {
   // this test requires C++17 mandatory return-value optimization (RVO)
-  std::array<A, 1> a = CGAL::fwd_make_array<A>(B());
-  std::array<double, 1> b = CGAL::fwd_make_array<double>(1u);
+  std::array<A, 1> a = CGAL::make_array<A>(B());
+  auto b = CGAL::make_array<double>(1u);
+  static_assert(std::is_same_v<decltype(b), std::array<double, 1>>);
   CGAL_USE(a);
   CGAL_USE(b);
   return 0;