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Implement LWG-4001 iota_view should provide empty #4193

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Merged
merged 2 commits into from
Nov 17, 2023
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Implement LWG-4001 iota_view should provide empty #4193

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c9dbba4
Implement LWG-4001.`iota_view` should provide `empty`
frederick-vs-ja Nov 14, 2023
0c9d1ab
Code review feedback.
StephanTLavavej Nov 14, 2023
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4 changes: 4 additions & 0 deletions stl/inc/ranges
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Original file line number Diff line number Diff line change
Expand Up @@ -1399,6 +1399,10 @@ namespace ranges {
}
}

_NODISCARD constexpr bool empty() const noexcept(noexcept(_Value == _Bound)) /* strengthened */ {
return _Value == _Bound;
}

#pragma warning(push)
#pragma warning(disable : 4146) // unary minus operator applied to unsigned type, result still unsigned
// clang-format off
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39 changes: 39 additions & 0 deletions tests/std/tests/P0896R4_views_iota/test.cpp
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Expand Up @@ -5,10 +5,12 @@
#include <cassert>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <ranges>
#include <type_traits>
#include <utility>
#include <vector>

using namespace std;

Expand All @@ -20,6 +22,14 @@ concept CanViewIota = requires(W w, B b) { views::iota(w, b); };
template <class R>
concept CanSize = requires(R& r) { ranges::size(r); };

template <class R>
concept CanEmpty = requires(const R& r) { ranges::empty(r); };

template <class R>
concept CanMemberEmpty = requires(const R& r) {
{ r.empty() } -> same_as<bool>;
};

struct empty_type {};

template <class T>
Expand Down Expand Up @@ -374,6 +384,16 @@ int main() {
views::iota(begin(as_const(objects)), end(objects)), objects, ranges::equal_to{}, identity{}, address));
assert(ranges::equal(
views::iota(begin(objects), end(as_const(objects))), objects, ranges::equal_to{}, identity{}, address));

using FirstConstIota = decltype(views::iota(begin(as_const(objects)), end(objects)));
static_assert(CanEmpty<FirstConstIota>);
static_assert(CanMemberEmpty<FirstConstIota>);
static_assert(noexcept(declval<const FirstConstIota&>().empty())); // strengthened

using SecondConstIota = decltype(views::iota(begin(objects), end(as_const(objects))));
static_assert(CanEmpty<SecondConstIota>);
static_assert(CanMemberEmpty<SecondConstIota>);
static_assert(noexcept(declval<const SecondConstIota&>().empty())); // strengthened
}
{
// Iterator and sentinel of a non-common range
Expand All @@ -387,6 +407,25 @@ int main() {
auto r = views::iota(ranges::begin(f), ranges::end(f));

assert(ranges::equal(r, even_ints, ranges::equal_to{}, deref));

using FilteredIota = decltype(r);
static_assert(CanEmpty<FilteredIota>);
static_assert(CanMemberEmpty<FilteredIota>);
}
// LWG-4001 iota_view should provide empty
{
using BackInsertingIota = decltype(views::iota(back_inserter(declval<vector<int>&>())));
static_assert(CanEmpty<BackInsertingIota>);
static_assert(CanMemberEmpty<BackInsertingIota>);
static_assert(noexcept(declval<const BackInsertingIota&>().empty())); // strengthened

constexpr auto test_back_inserting_iota_nonempty = [] {
vector<int> v;
auto vw = views::iota(back_inserter(v));
return !vw.empty();
};
assert(test_back_inserting_iota_nonempty());
static_assert(test_back_inserting_iota_nonempty());
}

test_difference();
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