[libcxx-commits] [PATCH] D57403: Extending make_shared to Support Arrays (Partially) - P0674R1

[Zoe Carver via Phabricator via libcxx-commits]

zoecarver created this revision.
zoecarver added a reviewer: EricWF.
Herald added subscribers: libcxx-commits, ldionne, christof.

Hi there,

I am a new contributor to libc++, so this patch will probably need some help. This patch incorporates some of the details highlighted in P0674R1 <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0674r1.html>. If all goes well, I will submit another one (or update this one) with the rest of the changes.

**Example**

  shared_ptr<double[1024]> p = make_shared<double[1024]>();

**Questions**

1. Is it okay to define `__shared_ptr_emplace__destroy`, a helper function, where and how I did?
2. Was removing `is_constructible<_Tp, _Args...>::value` okay (see comment in code)?
3. What are the next steps? Do I need to write more tests? Do I need to write some documentation?


Repository:
  rCXX libc++

https://reviews.llvm.org/D57403

Files:
  include/memory
  test/libcxx/memory/shared_ptr_array.pass.cpp


Index: test/libcxx/memory/shared_ptr_array.pass.cpp
===================================================================
--- test/libcxx/memory/shared_ptr_array.pass.cpp
+++ test/libcxx/memory/shared_ptr_array.pass.cpp
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+
+// <memory>
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+#include <memory>
+#include <string>
+
+#include "test_macros.h"
+#include "min_allocator.h"
+#include "test_allocator.h"
+
+template <typename T>
+void test_make_shared()
+{
+    std::shared_ptr<T[64]> foo = std::make_shared<T[64]>();
+    std::shared_ptr<T[64]> bar(foo);
+    assert(typeid(**foo) == typeid(T) && "Type is not the same");
+    assert(typeid(**bar) == typeid(T) && "Type is not the same");
+}
+
+
+int main()
+{
+    test_make_shared<char>();
+    test_make_shared<int>();
+    test_make_shared<std::string>();
+}
Index: include/memory
===================================================================
--- include/memory
+++ include/memory
@@ -3702,11 +3702,25 @@
     _Tp* get() _NOEXCEPT {return _VSTD::addressof(__data_.second());}
 };
 
+template <typename _Tp>
+void
+__shared_ptr_emplace__destroy(_Tp& t)
+{
+    t.~_Tp();
+}
+
+template <typename _Tp, std::size_t _N>
+void
+__shared_ptr_emplace__destroy(_Tp (&t)[_N])
+{
+    for (auto i = _N; i > 0; i--) __shared_ptr_emplace__destroy(t[i]);
+}
+
 template <class _Tp, class _Alloc>
 void
 __shared_ptr_emplace<_Tp, _Alloc>::__on_zero_shared() _NOEXCEPT
 {
-    __data_.second().~_Tp();
+    __shared_ptr_emplace__destroy(__data_.second());
 }
 
 template <class _Tp, class _Alloc>
@@ -4340,7 +4354,8 @@
 shared_ptr<_Tp>
 shared_ptr<_Tp>::allocate_shared(const _Alloc& __a, _Args&& ...__args)
 {
-    static_assert( is_constructible<_Tp, _Args...>::value, "Can't construct object in allocate_shared" );
+    // XXX is it okay to delete the line below? It seems like it is only checking if _Tp is an array.
+    // static_assert( is_constructible<_Tp, _Args...>::value, "Can't construct object in allocate_shared" );
     typedef __shared_ptr_emplace<_Tp, _Alloc> _CntrlBlk;
     typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
     typedef __allocator_destructor<_A2> _D2;
@@ -4699,11 +4714,7 @@
 
 template<class _Tp, class ..._Args>
 inline _LIBCPP_INLINE_VISIBILITY
-typename enable_if
-<
-    !is_array<_Tp>::value,
-    shared_ptr<_Tp>
->::type
+shared_ptr<_Tp>
 make_shared(_Args&& ...__args)
 {
     return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);


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