`<ranges>`: list-initialization is misused

[hewillk]

Non-list-initialization (parentheses) and list-initialization (curly braces) styles are mixed in the <ranges>, however, the latter does not provide any observable benefit and may bring potential issues.
We should use non-list-initialization consistently, as the standard does.

#include <ranges>
#include <initializer_list>
#include <utility>

struct I {
  using difference_type = int;
  using value_type = int;
  I(std::initializer_list<int*>) = delete;
  I(int*);
  int operator*() const;
  I& operator++();
  I operator++(int);
};

struct R {
  int* begin();
  I begin() const;
  std::unreachable_sentinel_t end() const;
};

int main() {
  auto r = R{} | std::views::transform(std::identity{});
  decltype(std::as_const(r).begin()) c = r.begin();
}

https://godbolt.org/z/89eo678qd

[hewillk]

move_sentinel has the same issue. (since these bugs are in the same category, I'm not going to open new ones.)

STL/stl/inc/iterator

Lines 193 to 197 in 5aae678

	template <class _Se2>
	requires convertible_to<const _Se2&, _Se>
	constexpr move_sentinel(const move_sentinel<_Se2>& _Val)
	noexcept(is_nothrow_constructible_v<_Se, const _Se2&>) // strengthened
	: _Last{_Val._Get_last()} {}

#include <iterator>

struct Sentinel {
  Sentinel() = default;
  Sentinel(std::initializer_list<int*>) = delete;
  Sentinel(int*);
};

int main() {
  std::move_sentinel<Sentinel> s(std::move_sentinel<int*>{});
}

https://godbolt.org/z/PMq8snb59

[StephanTLavavej]

Thanks for reporting this issue! I've edited your description to use the Standard's term "non-list-initialization" (often seen as "direct-non-list-initialization"), and clarified that this refers to parentheses, while list-initialization refers to curly braces. ("Braces" is often interpreted by Americans as referring to curly braces {}).