Test for C++20 p0858 - ConstexprIterator requirements.

[Ed Smith-Rowland via libstdc++]

On 6/1/19 2:42 PM, Ville Voutilainen wrote:
> On Sat, 1 Jun 2019 at 21:09, Ed Smith-Rowland <3dw4rd@verizon.net> wrote:
>> On 5/31/19 6:29 PM, Ville Voutilainen wrote:
>>> On Sat, 1 Jun 2019 at 01:24, Ed Smith-Rowland via libstdc++
>>> <libstdc++@gcc.gnu.org> wrote:
>>>> Greetings,
>>>>
>>>> Iterators for <array> and <string_view> are usabe in a constexpr context
>>>> since C++2017.
>>>>
>>>> This just adds a compile test to make sure and check a box for C++20
>>>> p0858 - ConstexprIterator requirements.
>>> Those tests don't use the iterators in a constexpr context. To do
>>> that, maybe do those std::copy operations
>>> in a constexpr function and then initialize a constexpr variable with
>>> the result of a call to that function?
>> Thanks Ville,
>>
>> I had completely forgotten to make these test functions constexpr - FIXED.
> .but that doesn't enforce a constexpr context. If you add another
> function that calls these functions
> and initializes a constexpr variable, then we have the enforcement I
> seek. Such as
>
> void test2()
> {
>      constexpr char x = test();
> }
>
Ok, third time's a charm.

I was brain dead about the constexpr patch.?? I'm now setting a constexpr 
variable from test() in a caller.

But static_assert is a constexpr context no?

Ed


-------------- next part --------------
2019-06-03  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Test for C++20 p0858 - ConstexprIterator requirements.
	* testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc:
	New test.
	* testsuite/23_containers/array/requirements/constexpr_iter.cc:
	New test.

-------------- next part --------------
Index: testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc
===================================================================
--- testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc	(nonexistent)
+++ testsuite/21_strings/basic_string_view/requirements/constexpr_iter.cc	(working copy)
@@ -0,0 +1,43 @@
+// { dg-do compile { target c++2a } }
+//
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <string_view>
+#include <array>
+
+constexpr char
+test()
+{
+  constexpr std::string_view hw("Hello, World!");
+  static_assert('H' == *hw.begin());
+  auto ch = hw[4];
+  static_assert('W' == *(hw.cbegin() + 7));
+
+#if __cplusplus > 201703L
+  std::array<int, hw.size()> a2{{0,0,0,0,0,0,0,0,0,0,0,0,0}};
+  std::copy(hw.begin(), hw.end(), a2.begin());
+#endif
+
+  return *(hw.cbegin() + 3);
+}
+
+void
+run_test()
+{
+  constexpr char ch = test();
+}
Index: testsuite/23_containers/array/requirements/constexpr_iter.cc
===================================================================
--- testsuite/23_containers/array/requirements/constexpr_iter.cc	(nonexistent)
+++ testsuite/23_containers/array/requirements/constexpr_iter.cc	(working copy)
@@ -0,0 +1,42 @@
+// { dg-do compile { target c++2a } }
+//
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <array>
+
+constexpr int
+test()
+{
+  constexpr std::array<int, 3> a1{{1, 2, 3}};
+  static_assert(1 == *a1.begin());
+  auto n = a1[0] * a1[1]* a1[2];
+  static_assert(1 == *a1.cbegin());
+
+#if __cplusplus > 201703L
+  std::array<int, 3> a2{{0, 0, 0}};
+  std::copy(a1.begin(), a1.end(), a2.begin());
+#endif
+
+  return n;
+}
+
+void
+run_test()
+{
+  constexpr int n = test();
+}