This hasn't been finally approved by LWG yet, but everybody seems to be
in favour of it. I think I'll push this soon.
Tested x86_64-linux.
-- >8 --
This implements the proposed resolution of LWG 4016, so that
std::ranges::to does not use std::back_inserter and std::inserter.
Instead it inserts at the back of the container directly, using
the first supported one of emplace_back, push_back, emplace, and insert.
Using emplace avoids creating a temporary that has to be moved into the
container, for cases where the source range and the destination
container do not have the same value type.
libstdc++-v3/ChangeLog:
* include/std/ranges (__detail::__container_insertable): Remove.
(__detail::__container_inserter): Remove.
(ranges::to): Use emplace_back or emplace, as per LWG 4016.
* testsuite/std/ranges/conv/1.cc (Cont4, test_2_1_4): Check for
use of emplace_back and emplace.
---
libstdc++-v3/include/std/ranges | 50 +++----
libstdc++-v3/testsuite/std/ranges/conv/1.cc | 149 ++++++++++++++++----
2 files changed, 144 insertions(+), 55 deletions(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 9d4c2e01c4d..afd0a38e0cf 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -9229,26 +9229,6 @@ namespace __detail
{ __c.max_size() } -> same_as<decltype(__n)>;
};
- template<typename _Container, typename _Ref>
- constexpr bool __container_insertable
- = requires(_Container& __c, _Ref&& __ref) {
- typename _Container::value_type;
- requires (
- requires { __c.push_back(std::forward<_Ref>(__ref)); }
- || requires { __c.insert(__c.end(), std::forward<_Ref>(__ref)); }
- );
- };
-
- template<typename _Ref, typename _Container>
- constexpr auto
- __container_inserter(_Container& __c)
- {
- if constexpr (requires { __c.push_back(std::declval<_Ref>()); })
- return std::back_inserter(__c);
- else
- return std::inserter(__c, __c.end());
- }
-
template<typename _Cont, typename _Range>
constexpr bool __toable = requires {
requires (!input_range<_Cont>
@@ -9301,17 +9281,33 @@ namespace __detail
std::forward<_Args>(__args)...);
else
{
- using __detail::__container_insertable;
- using __detail::__reservable_container;
using _RefT = range_reference_t<_Rg>;
static_assert(constructible_from<_Cont, _Args...>);
- static_assert(__container_insertable<_Cont, _RefT>);
_Cont __c(std::forward<_Args>(__args)...);
- if constexpr (sized_range<_Rg> && __reservable_container<_Cont>)
+ if constexpr (sized_range<_Rg>
+ && __detail::__reservable_container<_Cont>)
__c.reserve(static_cast<range_size_t<_Cont>>(ranges::size(__r)));
- auto __ins = __detail::__container_inserter<_RefT>(__c);
- for (auto&& __e : __r)
- *__ins++ = std::forward<decltype(__e)>(__e);
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4016. container-insertable checks do not match what
+ // container-inserter does
+ auto __it = ranges::begin(__r);
+ const auto __sent = ranges::end(__r);
+ while (__it != __sent)
+ {
+ if constexpr (requires { __c.emplace_back(*__it); })
+ __c.emplace_back(*__it);
+ else if constexpr (requires { __c.push_back(*__it); })
+ __c.push_back(*__it);
+ else
+ {
+ auto __end = __c.end();
+ if constexpr (requires { __c.emplace(__end, *__it); })
+ __end = __c.emplace(__end, *__it);
+ else
+ __end = __c.insert(__end, *__it);
+ }
+ ++__it;
+ }
return __c;
}
}
diff --git a/libstdc++-v3/testsuite/std/ranges/conv/1.cc
b/libstdc++-v3/testsuite/std/ranges/conv/1.cc
index 4b6814b1add..b5f861dedb3 100644
--- a/libstdc++-v3/testsuite/std/ranges/conv/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/conv/1.cc
@@ -203,33 +203,51 @@ test_2_1_3()
VERIFY( c2.c.get_allocator() == Alloc(78) );
}
-template<typename C, bool UsePushBack = true>
+enum AppendKind { None, EmplaceBack, PushBack, Emplace, Insert };
+
+template<typename C, AppendKind Kind>
struct Cont4
{
- using value_type = typename C::value_type;
-
// Only support construction with no args or an allocator.
- // This forces the use of either push_back or insert to fill the container.
+ // This forces the use of either emplace_back, push_back, emplace or insert.
Cont4() { }
Cont4(typename C::allocator_type a) : c(a) { }
- // Satisfying container-insertable requires either this ...
template<typename T>
- requires UsePushBack
+ requires (Kind <= EmplaceBack)
+ && requires(C& c, T&& t) { c.emplace_back(std::forward<T>(t)); }
+ void
+ emplace_back(T&& t)
+ {
+ kind = EmplaceBack;
+ c.emplace_back(std::forward<T>(t));
+ }
+
+ template<typename T>
+ requires (Kind <= PushBack)
&& requires(C& c, T&& t) { c.push_back(std::forward<T>(t)); }
void
push_back(T&& t)
{
+ kind = PushBack;
c.push_back(std::forward<T>(t));
- used_push_back = true;
}
- // ... or this:
+ template<typename T>
+ requires (Kind <= Emplace)
+ && requires(C& c, T&& t) { c.emplace(c.end(), std::forward<T>(t)); }
+ typename C::iterator
+ emplace(typename C::iterator, T&& t)
+ {
+ kind = Emplace;
+ return c.emplace(c.end(), std::forward<T>(t));
+ }
+
template<typename T>
typename C::iterator
insert(typename C::iterator, T&& t)
{
- used_push_back = false;
+ kind = Insert;
return c.insert(c.end(), std::forward<T>(t));
}
@@ -254,7 +272,7 @@ struct Cont4
auto max_size() const { return c.max_size(); }
C c;
- bool used_push_back = false;
+ AppendKind kind{};
bool used_reserve = false;
};
@@ -265,38 +283,113 @@ test_2_1_4()
// container-insertable<C, range_reference_t<R>>
using Alloc = __gnu_test::uneq_allocator<int>;
+ using Alloc2 = __gnu_test::uneq_allocator<short>;
using V = std::vector<int, Alloc>;
+ using List = std::list<short, Alloc2>;
std::list<unsigned> l{1u, 2u, 3u};
- auto c = std::ranges::to<Cont4<V>>(l);
- static_assert(std::is_same_v<decltype(c), Cont4<V>>);
+ std::list<long> l2{4l, 5l, 6l};
+
+ // use vector::emplace_back and vector::reserve
+ auto c = std::ranges::to<Cont4<V, EmplaceBack>>(l);
+ static_assert(std::is_same_v<decltype(c), Cont4<V, EmplaceBack>>);
VERIFY( c.c == V(l.begin(), l.end()) );
- VERIFY( c.used_push_back );
+ VERIFY( c.kind == EmplaceBack );
VERIFY( c.used_reserve );
- std::list<long> l2{4l, 5l, 6l};
- auto c2 = std::ranges::to<Cont4<V>>(l2, Alloc(78));
- static_assert(std::is_same_v<decltype(c2), Cont4<V>>);
+ // use vector::emplace_back and vector::reserve
+ auto c2 = std::ranges::to<Cont4<V, EmplaceBack>>(l2, Alloc(78));
+ static_assert(std::is_same_v<decltype(c2), Cont4<V, EmplaceBack>>);
VERIFY( c2.c == V(l2.begin(), l2.end()) );
VERIFY( c2.c.get_allocator() == Alloc(78) );
- VERIFY( c2.used_push_back );
+ VERIFY( c2.kind == EmplaceBack );
VERIFY( c2.used_reserve );
- using Alloc2 = __gnu_test::uneq_allocator<short>;
- using List = std::list<short, Alloc2>;
- auto c3 = std::ranges::to<Cont4<List>>(c.c, Alloc2(99));
- static_assert(std::is_same_v<decltype(c3), Cont4<List>>);
+ // use list::emplace_back
+ auto c3 = std::ranges::to<Cont4<List, EmplaceBack>>(c.c, Alloc2(99));
+ static_assert(std::is_same_v<decltype(c3), Cont4<List, EmplaceBack>>);
VERIFY( c3.c == List(l.begin(), l.end()) );
VERIFY( c3.c.get_allocator() == Alloc(99) );
- VERIFY( c3.used_push_back );
+ VERIFY( c3.kind == EmplaceBack );
VERIFY( ! c3.used_reserve );
- auto c4 = std::ranges::to<Cont4<List, false>>(c.c, Alloc2(111));
- static_assert(std::is_same_v<decltype(c4), Cont4<List, false>>);
- VERIFY( c4.c == List(l.begin(), l.end()) );
- VERIFY( c4.c.get_allocator() == Alloc(111) );
- VERIFY( ! c4.used_push_back );
- VERIFY( ! c4.used_reserve );
+ // use vector::push_back and vector::reserve
+ auto c4 = std::ranges::to<Cont4<V, PushBack>>(l);
+ static_assert(std::is_same_v<decltype(c4), Cont4<V, PushBack>>);
+ VERIFY( c4.c == V(l.begin(), l.end()) );
+ VERIFY( c4.kind == PushBack );
+ VERIFY( c4.used_reserve );
+
+ // use vector::push_back and vector::reserve
+ auto c5 = std::ranges::to<Cont4<V, PushBack>>(l2, Alloc(78));
+ static_assert(std::is_same_v<decltype(c5), Cont4<V, PushBack>>);
+ VERIFY( c5.c == V(l2.begin(), l2.end()) );
+ VERIFY( c5.c.get_allocator() == Alloc(78) );
+ VERIFY( c5.kind == PushBack );
+ VERIFY( c5.used_reserve );
+
+ // use list::push_back
+ auto c6 = std::ranges::to<Cont4<List, PushBack>>(c.c, Alloc2(99));
+ static_assert(std::is_same_v<decltype(c6), Cont4<List, PushBack>>);
+ VERIFY( c6.c == List(l.begin(), l.end()) );
+ VERIFY( c6.c.get_allocator() == Alloc(99) );
+ VERIFY( c6.kind == PushBack );
+ VERIFY( ! c6.used_reserve );
+
+ // use vector::emplace and vector::reserve
+ auto c7 = std::ranges::to<Cont4<V, Emplace>>(l);
+ static_assert(std::is_same_v<decltype(c7), Cont4<V, Emplace>>);
+ VERIFY( c7.c == V(l.begin(), l.end()) );
+ VERIFY( c7.kind == Emplace );
+ VERIFY( c7.used_reserve );
+
+ // use vector::emplace and vector::reserve
+ auto c8 = std::ranges::to<Cont4<V, Emplace>>(l2, Alloc(78));
+ static_assert(std::is_same_v<decltype(c8), Cont4<V, Emplace>>);
+ VERIFY( c8.c == V(l2.begin(), l2.end()) );
+ VERIFY( c8.c.get_allocator() == Alloc(78) );
+ VERIFY( c8.kind == Emplace );
+ VERIFY( c8.used_reserve );
+
+ // use list::emplace
+ auto c9 = std::ranges::to<Cont4<List, Emplace>>(c.c, Alloc2(99));
+ static_assert(std::is_same_v<decltype(c9), Cont4<List, Emplace>>);
+ VERIFY( c9.c == List(l.begin(), l.end()) );
+ VERIFY( c9.c.get_allocator() == Alloc(99) );
+ VERIFY( c9.kind == Emplace );
+ VERIFY( ! c9.used_reserve );
+
+ // use vector::insert and vector::reserve
+ auto c10 = std::ranges::to<Cont4<V, Insert>>(l);
+ static_assert(std::is_same_v<decltype(c10), Cont4<V, Insert>>);
+ VERIFY( c10.c == V(l.begin(), l.end()) );
+ VERIFY( c10.kind == Insert );
+ VERIFY( c10.used_reserve );
+
+ // use vector::insert and vector::reserve
+ auto c11 = std::ranges::to<Cont4<V, Insert>>(l2, Alloc(78));
+ static_assert(std::is_same_v<decltype(c11), Cont4<V, Insert>>);
+ VERIFY( c11.c == V(l2.begin(), l2.end()) );
+ VERIFY( c11.c.get_allocator() == Alloc(78) );
+ VERIFY( c11.kind == Insert );
+ VERIFY( c11.used_reserve );
+
+ // use list::insert
+ auto c12 = std::ranges::to<Cont4<List, Insert>>(c.c, Alloc2(99));
+ static_assert(std::is_same_v<decltype(c12), Cont4<List, Insert>>);
+ VERIFY( c12.c == List(l.begin(), l.end()) );
+ VERIFY( c12.c.get_allocator() == Alloc(99) );
+ VERIFY( c12.kind == Insert );
+ VERIFY( ! c12.used_reserve );
+
+ struct NoCopyPls
+ {
+ NoCopyPls(int) { }
+ NoCopyPls(const NoCopyPls&) { throw; }
+ };
+
+ // Uses list::emplace_back(const int&) not list::push_back(NoCopyPls&&).
+ (void) std::ranges::to<std::list<NoCopyPls>>(l);
}
void
--
2.43.0
