On Thu, 30 Nov 2023 at 15:53, Jonathan Wakely wrote:
>
> Before pushing I'll fix the summary to say "LWG" instead of "LGW" (the
> airport code for London Gatwick!)
Pushed to trunk now.
>
> On Thu, 30 Nov 2023 at 15:51, Jonathan Wakely wrote:
> >
> > 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
> >
