libstdc++: Define C++20 range utilities and range factories

This adds another chunk of the <ranges> header.

The changes from P1456R1 (Move-only views) and P1862R1 (Range adaptors
for non-copyable iterators) are included, but not the changes from
P1870R1 (forwarding-range<T> is too subtle).

The tests for subrange and iota_view are poor and should be improved.

	* include/bits/regex.h (match_results): Specialize __enable_view_impl.
	* include/bits/stl_set.h (set): Likewise.
	* include/bits/unordered_set.h (unordered_set, unordered_multiset):
	Likewise.
	* include/debug/multiset.h (__debug::multiset): Likewise.
	* include/debug/set.h (__debug::set): Likewise.
	* include/debug/unordered_set (__debug::unordered_set)
	(__debug::unordered_multiset): Likewise.
	* include/std/ranges (ranges::view, ranges::enable_view)
	(ranges::view_interface, ranges::subrange, ranges::empty_view)
	(ranges::single_view, ranges::views::single, ranges::iota_view)
	(ranges::views::iota): Define for C++20.
	* testsuite/std/ranges/empty_view.cc: New test.
	* testsuite/std/ranges/iota_view.cc: New test.
	* testsuite/std/ranges/single_view.cc: New test.
	* testsuite/std/ranges/view.cc: New test.

From-SVN: r278370

libstdc++-v3/ChangeLog

+2019-11-17  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/bits/regex.h (match_results): Specialize __enable_view_impl.
+	* include/bits/stl_set.h (set): Likewise.
+	* include/bits/unordered_set.h (unordered_set, unordered_multiset):
+	Likewise.
+	* include/debug/multiset.h (__debug::multiset): Likewise.
+	* include/debug/set.h (__debug::set): Likewise.
+	* include/debug/unordered_set (__debug::unordered_set)
+	(__debug::unordered_multiset): Likewise.
+	* include/std/ranges (ranges::view, ranges::enable_view)
+	(ranges::view_interface, ranges::subrange, ranges::empty_view)
+	(ranges::single_view, ranges::views::single, ranges::iota_view)
+	(ranges::views::iota): Define for C++20.
+	* testsuite/std/ranges/empty_view.cc: New test.
+	* testsuite/std/ranges/iota_view.cc: New test.
+	* testsuite/std/ranges/single_view.cc: New test.
+	* testsuite/std/ranges/view.cc: New test.
+
 2019-11-16  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/ranges: Revert accidentally committed changes.

libstdc++-v3/include/bits/regex.h

@@ -2056,9 +2056,18 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	 match_results<_Bi_iter, _Alloc>& __rhs) noexcept
     { __lhs.swap(__rhs); }
 
-
 _GLIBCXX_END_NAMESPACE_CXX11
 
+#if __cplusplus > 201703L
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Bi_iter, typename _Alloc>
+    inline constexpr bool __enable_view_impl<match_results<_Bi_iter, _Alloc>>
+      = false;
+} // namespace ranges::__detail
+#endif // C++20
+
   // [28.11.2] Function template regex_match
   /**
    * @name Matching, Searching, and Replacing

libstdc++-v3/include/bits/stl_multiset.h

@@ -1039,6 +1039,16 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
       { return __set._M_t; }
     };
 
+#if __cplusplus > 201703L
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Key, typename _Compare, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<_GLIBCXX_STD_C::multiset<_Key, _Compare, _Alloc>>
+	= false;
+} // namespace ranges::__detail
+#endif // C++20
 #endif // C++17
 
 _GLIBCXX_END_NAMESPACE_VERSION

libstdc++-v3/include/bits/stl_set.h

@@ -1051,6 +1051,15 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
       _S_get_tree(_GLIBCXX_STD_C::multiset<_Val, _Cmp2, _Alloc>& __set)
       { return __set._M_t; }
     };
+#if __cplusplus > 201703L
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Key, typename _Compare, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<_GLIBCXX_STD_C::set<_Key, _Compare, _Alloc>> = false;
+} // namespace ranges::__detail
+#endif // C++20
 #endif // C++17
 
 _GLIBCXX_END_NAMESPACE_VERSION

libstdc++-v3/include/bits/unordered_set.h

@@ -1771,6 +1771,21 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
       _S_get_table(unordered_multiset<_Val, _Hash2, _Eq2, _Alloc>& __set)
       { return __set._M_h; }
     };
+
+#if __cplusplus > 201703L
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Val, typename _Hash, typename _Eq, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<_GLIBCXX_STD_C::unordered_set<_Val, _Hash, _Eq,
+						       _Alloc>> = false;
+  template<typename _Val, typename _Hash, typename _Eq, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<_GLIBCXX_STD_C::unordered_multiset<_Val, _Hash, _Eq,
+							    _Alloc>> = false;
+} // namespace ranges::__detail
+#endif // C++20
 #endif // C++17
 
 _GLIBCXX_END_NAMESPACE_VERSION

libstdc++-v3/include/debug/multiset.h

@@ -630,6 +630,19 @@ namespace __debug
     { return __x.swap(__y); }
 
 } // namespace __debug
+
+#if __cplusplus > 201703L
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Key, typename _Compare, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<std::__debug::multiset<_Key, _Compare, _Alloc>>
+	= false;
+} // namespace ranges::__detail
+_GLIBCXX_END_NAMESPACE_VERSION
+#endif // C++20
 } // namespace std
 
 #endif

libstdc++-v3/include/debug/set.h

@@ -641,6 +641,18 @@ namespace __debug
     { return __x.swap(__y); }
 
 } // namespace __debug
+
+#if __cplusplus > 201703L
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Key, typename _Compare, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<std::__debug::set<_Key, _Compare, _Alloc>> = false;
+} // namespace ranges::__detail
+_GLIBCXX_END_NAMESPACE_VERSION
+#endif // C++20
 } // namespace std
 
 #endif

libstdc++-v3/include/debug/unordered_set

@@ -1183,6 +1183,22 @@ namespace __debug
     { return !(__x == __y); }
 
 } // namespace __debug
+#if __cplusplus > 201703L
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+namespace ranges::__detail
+{
+  template<typename _Tp> inline constexpr bool __enable_view_impl;
+  template<typename _Val, typename _Hash, typename _Eq, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<std::__debug::unordered_set<_Val, _Hash, _Eq, _Alloc>>
+	= false;
+  template<typename _Val, typename _Hash, typename _Eq, typename _Alloc>
+    inline constexpr bool
+      __enable_view_impl<std::__debug::unordered_multiset<_Val, _Hash, _Eq,
+							  _Alloc>> = false;
+} // namespace ranges::__detail
+_GLIBCXX_END_NAMESPACE_VERSION
+#endif // C++20
 } // namespace std
 
 #endif // C++11

libstdc++-v3/testsuite/std/ranges/empty_view.cc

+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <ranges>
+
+static_assert(std::ranges::view<std::ranges::empty_view<int>>);
+
+std::ranges::empty_view<int> e;
+static_assert(std::ranges::empty(e));
+static_assert(0 == e.size());
+
+static_assert(e.begin() == nullptr);
+static_assert(e.end() == nullptr);
+static_assert(e.data() == nullptr);
+static_assert(e.empty());
+
+static_assert(begin(e) == nullptr);
+static_assert(end(e) == nullptr);

libstdc++-v3/testsuite/std/ranges/iota_view.cc

+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <ranges>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  int vals[5] = { };
+  int* out = vals;
+  for (int i : std::ranges::iota_view{1, 4})
+    *out++ = i;
+  VERIFY(out == vals + 3);
+  VERIFY(vals[0] == 1);
+  VERIFY(vals[1] == 2);
+  VERIFY(vals[2] == 3);
+  VERIFY(vals[3] == 0);
+}
+
+void
+test02()
+{
+  auto v = std::ranges::views::iota(4);
+  auto it = v.begin();
+  VERIFY( *it == 4 );
+  ++it;
+  VERIFY( *it == 5 );
+  it++;
+  VERIFY( *it == 6 );
+}
+
+void
+test03()
+{
+  auto v = std::ranges::views::iota(10, 15);
+  auto it = v.begin();
+  VERIFY( *it == 10 );
+  it += 2;
+  VERIFY( *it == 12 );
+  it += 2;
+  VERIFY( *it == 14 );
+  ++it;
+  VERIFY( it == v.end() );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}

libstdc++-v3/testsuite/std/ranges/single_view.cc

+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <ranges>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::ranges::single_view s{4};
+  static_assert(std::same_as<std::ranges::range_value_t<decltype(s)>, int>);
+  static_assert(std::ranges::size(s) == 1);
+
+  int count = 0;
+  for (auto i : s)
+    ++count;
+  VERIFY(count == 1);
+  VERIFY(*std::ranges::begin(s) == 4);
+}
+
+void
+test02()
+{
+  std::ranges::single_view<long> s2;
+  static_assert(std::same_as<std::ranges::range_value_t<decltype(s2)>, long>);
+  static_assert(std::ranges::size(s2) == 1);
+
+  int count = 0;
+  for (auto l : s2)
+    ++count;
+  VERIFY(count == 1);
+  VERIFY(*std::ranges::begin(s2) == 0L);
+}
+
+void
+test03()
+{
+  auto s3 = std::ranges::views::single('a');
+  static_assert(std::same_as<std::ranges::range_value_t<decltype(s3)>, char>);
+  static_assert(std::ranges::size(s3) == 1);
+  VERIFY(*std::ranges::begin(s3) == 'a');
+}
+
+int main()
+{
+  test01();
+  test02();
+  test03();
+}

libstdc++-v3/testsuite/std/ranges/view.cc

+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <ranges>
+#include <vector>
+#include <set>
+#include <unordered_set>
+#include <regex>
+#include <testsuite_iterators.h>
+
+static_assert(std::ranges::view<std::vector<int>>);
+static_assert(!std::ranges::view<const std::vector<int>>);
+static_assert(!std::ranges::view<std::initializer_list<int>>);
+static_assert(!std::ranges::view<const std::initializer_list<int>>);
+static_assert(!std::ranges::view<std::set<int>>);
+static_assert(!std::ranges::view<const std::set<int>>);
+static_assert(!std::ranges::view<std::multiset<int>>);
+static_assert(!std::ranges::view<std::unordered_set<int>>);
+static_assert(!std::ranges::view<std::unordered_multiset<int>>);
+static_assert(!std::ranges::view<std::cmatch>);
+
+// const test_random_access_range<T> is not a range:
+static_assert(!std::ranges::view<__gnu_test::test_random_access_range<int>>);
+
+template<typename T>
+struct test_view
+: __gnu_test::test_random_access_range<T>, std::ranges::view_base
+{
+  // views must be default-initializable:
+  test_view() : __gnu_test::test_random_access_range<T>(nullptr, nullptr) { }
+};
+
+static_assert(std::ranges::view<test_view<int>>);
+
+template<>
+constexpr bool std::ranges::enable_view<test_view<long>> = false;
+
+static_assert(!std::ranges::view<test_view<long>>);