From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: Re: [committed 2/3] libstdc++: Constrain std::make_optional
Date: Mon, 6 Jul 2020 22:08:04 +0100 [thread overview]
Message-ID: <20200706210804.GF4137376@redhat.com> (raw)
In-Reply-To: <20200706210646.GD4137376@redhat.com>
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On 06/07/20 22:06 +0100, Jonathan Wakely wrote:
>The standard rquires that std::make_optional is constrained similarly to
>the std::optional constructors, which our implementation fails to do.
>
>As a conforming extension this also adds a noexcept-specifier to each
>std::make_optional overload.
>
>libstdc++-v3/ChangeLog:
>
> * include/std/optional (make_optional): Add enable_if
> constraints and noexcept-specifier to each overload.
> * testsuite/20_util/optional/make_optional-2.cc: New test.
>
>
>Tested powerpc64le-linux, committed to trunk.
And with the patch attached this time ...
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commit bcfe4681f9be68f96f0610f30356510ff518806b
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jul 6 21:54:12 2020 +0100
libstdc++: Constrain std::make_optional
The standard rquires that std::make_optional is constrained similarly to
the std::optional constructors, which our implementation fails to do.
As a conforming extension this also adds a noexcept-specifier to each
std::make_optional overload.
libstdc++-v3/ChangeLog:
* include/std/optional (make_optional): Add enable_if
constraints and noexcept-specifier to each overload.
* testsuite/20_util/optional/make_optional-2.cc: New test.
diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index 785c434412d..24821f81d0f 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1220,19 +1220,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
swap(optional<_Tp>&, optional<_Tp>&) = delete;
template<typename _Tp>
- constexpr optional<decay_t<_Tp>>
+ constexpr
+ enable_if_t<is_constructible_v<decay_t<_Tp>, _Tp>,
+ optional<decay_t<_Tp>>>
make_optional(_Tp&& __t)
- { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
+ noexcept(is_nothrow_constructible_v<optional<decay_t<_Tp>>, _Tp>)
+ { return optional<decay_t<_Tp>>{ std::forward<_Tp>(__t) }; }
- template<typename _Tp, typename ..._Args>
- constexpr optional<_Tp>
+ template<typename _Tp, typename... _Args>
+ constexpr
+ enable_if_t<is_constructible_v<_Tp, _Args...>,
+ optional<_Tp>>
make_optional(_Args&&... __args)
- { return optional<_Tp> { in_place, std::forward<_Args>(__args)... }; }
+ noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
+ { return optional<_Tp>{ in_place, std::forward<_Args>(__args)... }; }
- template<typename _Tp, typename _Up, typename ..._Args>
- constexpr optional<_Tp>
+ template<typename _Tp, typename _Up, typename... _Args>
+ constexpr
+ enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
+ optional<_Tp>>
make_optional(initializer_list<_Up> __il, _Args&&... __args)
- { return optional<_Tp> { in_place, __il, std::forward<_Args>(__args)... }; }
+ noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
+ { return optional<_Tp>{ in_place, __il, std::forward<_Args>(__args)... }; }
// Hash.
diff --git a/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc b/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc
new file mode 100644
index 00000000000..65a1fc78d80
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/optional/make_optional-2.cc
@@ -0,0 +1,94 @@
+// { dg-do compile { target c++17 } }
+
+// Copyright (C) 2020 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 <optional>
+
+int i;
+
+struct Cont
+{
+ Cont() noexcept;
+ Cont(Cont&&) noexcept;
+ Cont(const Cont&);
+ Cont(int);
+ Cont(std::initializer_list<int>, int) noexcept;
+ Cont(std::initializer_list<int>, const char*);
+};
+const Cont c{};
+
+template<typename T, typename = void>
+ struct can_make_optional1
+ : std::false_type
+ { };
+
+template<typename T>
+ struct can_make_optional1<T,
+ std::void_t<decltype(std::make_optional(std::declval<T>()))>>
+ : std::true_type
+ { };
+
+static_assert( can_make_optional1<int>::value );
+static_assert( noexcept(std::make_optional(1)) );
+static_assert( can_make_optional1<int&>::value );
+static_assert( noexcept(std::make_optional(i)) );
+static_assert( ! can_make_optional1<void>::value );
+static_assert( can_make_optional1<Cont>::value );
+static_assert( noexcept(std::make_optional(Cont{})) );
+static_assert( can_make_optional1<Cont>::value );
+static_assert( ! noexcept(std::make_optional(c)) );
+
+template<typename T, typename Arg, typename = void>
+ struct can_make_optional2
+ : std::false_type
+ { };
+
+template<typename T, typename Arg>
+ struct can_make_optional2<T, Arg,
+ std::void_t<decltype(std::make_optional<T>(std::declval<Arg>()))>>
+ : std::true_type
+ { };
+
+static_assert( can_make_optional2<int, int>::value );
+static_assert( noexcept(std::make_optional<int>(1)) );
+static_assert( can_make_optional2<int, int&>::value );
+static_assert( noexcept(std::make_optional(i)) );
+static_assert( ! can_make_optional2<void, void>::value );
+static_assert( can_make_optional2<Cont, Cont>::value );
+static_assert( noexcept(std::make_optional<Cont>({})) );
+static_assert( can_make_optional2<Cont, const Cont&>::value );
+static_assert( ! noexcept(std::make_optional(c)) );
+static_assert( can_make_optional2<Cont, int>::value );
+static_assert( ! noexcept(std::make_optional<Cont>(1)) );
+
+template<typename T, typename Arg, typename = void>
+ struct can_make_optional3
+ : std::false_type
+ { };
+
+template<typename T, typename Arg>
+ struct can_make_optional3<T, Arg,
+ std::void_t<decltype(std::make_optional<T>({1,2}, std::declval<Arg>()))>>
+ : std::true_type
+ { };
+
+static_assert( can_make_optional3<Cont, int>::value );
+static_assert( noexcept(std::make_optional<Cont>({1,2}, 1)) );
+static_assert( can_make_optional3<Cont, char*>::value );
+static_assert( ! noexcept(std::make_optional<Cont>({1,2}, "")) );
+static_assert( !can_make_optional3<Cont, int*>::value );
prev parent reply other threads:[~2020-07-06 21:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-06 21:05 [committed 1/3] libstdc++: Add noexcept to std::optional initialization (PR 96036) Jonathan Wakely
2020-07-06 21:06 ` [committed 2/3] libstdc++: Constrain std::make_optional Jonathan Wakely
2020-07-06 21:07 ` [committed 3/3] libstdc++: Cleanup whitespace and type trait usage in <optional> Jonathan Wakely
2020-07-06 21:08 ` Jonathan Wakely [this message]
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