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[2026-03 LWG Motion 12] P3059R2 Making user-defined constructors of view iterators/sentinels private #8911

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[2026-03 LWG Motion 12] P3059R2 Making user-defined constructors of view iterators/sentinels private #8911

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82 changes: 41 additions & 41 deletions source/ranges.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -3119,7 +3119,8 @@
requires @\exposconcept{weakly-equality-comparable-with}@<W, Bound> && @\libconcept{copyable}@<W>
struct iota_view<W, Bound>::@\exposid{iterator}@ {
private:
W @\exposid{value_}@ = W(); // \expos
W @\exposid{value_}@ = W(); // \expos
constexpr explicit @\exposid{iterator}@(W value); // \expos

public:
using iterator_concept = @\seebelow@;
Expand All @@ -3129,7 +3130,6 @@
using difference_type = @\placeholdernc{IOTA-DIFF-T}@(W);

@\exposid{iterator}@() requires @\libconcept{default_initializable}@<W> = default;
constexpr explicit @\exposid{iterator}@(W value);

constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>);

Expand Down Expand Up @@ -3500,11 +3500,11 @@
requires @\exposconcept{weakly-equality-comparable-with}@<W, Bound> && @\libconcept{copyable}@<W>
struct iota_view<W, Bound>::@\exposid{sentinel}@ {
private:
Bound @\exposid{bound_}@ = Bound(); // \expos
Bound @\exposid{bound_}@ = Bound(); // \expos
constexpr explicit @\exposid{sentinel}@(Bound bound); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(Bound bound);

friend constexpr bool operator==(const @\exposid{iterator}@& x, const @\exposid{sentinel}@& y);

Expand Down Expand Up @@ -4100,8 +4100,6 @@
using difference_type = ptrdiff_t;
using value_type = Val;

constexpr explicit @\exposid{iterator}@(basic_istream_view& parent) noexcept;

@\exposid{iterator}@(const @\exposid{iterator}@&) = delete;
@\exposid{iterator}@(@\exposid{iterator}@&&) = default;

Expand All @@ -4116,7 +4114,8 @@
friend bool operator==(const @\exposid{iterator}@& x, default_sentinel_t);

private:
basic_istream_view* @\exposid{parent_}@; // \expos
constexpr explicit @\exposid{iterator}@(basic_istream_view& parent) noexcept; // \expos
basic_istream_view* @\exposid{parent_}@; // \expos
};
}
\end{codeblock}
Expand Down Expand Up @@ -4880,8 +4879,9 @@
requires @\libconcept{view}@<V> && is_object_v<Pred>
class filter_view<V, Pred>::@\exposid{iterator}@ {
private:
iterator_t<V> @\exposid{current_}@ = iterator_t<V>(); // \expos
filter_view* @\exposid{parent_}@ = nullptr; // \expos
iterator_t<V> @\exposid{current_}@ = iterator_t<V>(); // \expos
filter_view* @\exposid{parent_}@ = nullptr; // \expos
constexpr @\exposid{iterator}@(filter_view& parent, iterator_t<V> current); // \expos

public:
using iterator_concept = @\seebelownc@;
Expand All @@ -4890,7 +4890,6 @@
using difference_type = range_difference_t<V>;

@\exposid{iterator}@() requires @\libconcept{default_initializable}@<iterator_t<V>> = default;
constexpr @\exposid{iterator}@(filter_view& parent, iterator_t<V> current);

constexpr const iterator_t<V>& base() const & noexcept;
constexpr iterator_t<V> base() &&;
Expand Down Expand Up @@ -5135,11 +5134,11 @@
requires @\libconcept{view}@<V> && is_object_v<Pred>
class filter_view<V, Pred>::@\exposid{sentinel}@ {
private:
sentinel_t<V> @\exposid{end_}@ = sentinel_t<V>(); // \expos
sentinel_t<V> @\exposid{end_}@ = sentinel_t<V>(); // \expos
constexpr explicit @\exposid{sentinel}@(filter_view& parent); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(filter_view& parent);

constexpr sentinel_t<V> base() const;

Expand Down Expand Up @@ -5380,10 +5379,11 @@
template<bool Const>
class transform_view<V, F>::@\exposid{iterator}@ {
private:
using @\exposidnc{Parent}@ = @\exposidnc{maybe-const}@<Const, transform_view>; // \expos
using @\exposidnc{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos
iterator_t<@\exposidnc{Base}@> @\exposid{current_}@ = iterator_t<@\exposidnc{Base}@>(); // \expos
@\exposidnc{Parent}@* @\exposid{parent_}@ = nullptr; // \expos
using @\exposidnc{Parent}@ = @\exposidnc{maybe-const}@<Const, transform_view>; // \expos
using @\exposidnc{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos
iterator_t<@\exposidnc{Base}@> @\exposid{current_}@ = iterator_t<@\exposidnc{Base}@>(); // \expos
@\exposidnc{Parent}@* @\exposid{parent_}@ = nullptr; // \expos
constexpr @\exposid{iterator}@(@\exposid{Parent}@& parent, iterator_t<@\exposidnc{Base}@> current); // \expos

public:
using iterator_concept = @\seebelownc@;
Expand All @@ -5393,7 +5393,6 @@
using difference_type = range_difference_t<@\exposid{Base}@>;

@\exposid{iterator}@() requires @\libconcept{default_initializable}@<iterator_t<@\exposid{Base}@>> = default;
constexpr @\exposid{iterator}@(@\exposid{Parent}@& parent, iterator_t<@\exposid{Base}@> current);
constexpr @\exposid{iterator}@(@\exposid{iterator}@<!Const> i)
requires Const && @\libconcept{convertible_to}@<iterator_t<V>, iterator_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -5767,10 +5766,10 @@
using @\exposid{Parent}@ = @\exposid{maybe-const}@<Const, transform_view>; // \expos
using @\exposid{Base}@ = @\exposid{maybe-const}@<Const, V>; // \expos
sentinel_t<@\exposid{Base}@> @\exposid{end_}@ = sentinel_t<@\exposid{Base}@>(); // \expos
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end);
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> i)
requires Const && @\libconcept{convertible_to}@<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -6109,10 +6108,10 @@
template<bool OtherConst>
using @\exposid{CI}@ = counted_iterator<iterator_t<@\exposid{maybe-const}@<OtherConst, V>>>; // \expos
sentinel_t<@\exposid{Base}@> @\exposid{end_}@ = sentinel_t<@\exposid{Base}@>(); // \expos
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end);
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> s)
requires Const && @\libconcept{convertible_to}@<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -6292,14 +6291,14 @@
@\libconcept{indirect_unary_predicate}@<const Pred, iterator_t<V>>
template<bool Const>
class take_while_view<V, Pred>::@\exposidnc{sentinel}@ {
using @\exposidnc{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos
using @\exposidnc{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos

sentinel_t<@\exposidnc{Base}@> @\exposid{end_}@ = sentinel_t<@\exposidnc{Base}@>(); // \expos
const Pred* @\exposid{pred_}@ = nullptr; // \expos
sentinel_t<@\exposidnc{Base}@> @\exposid{end_}@ = sentinel_t<@\exposidnc{Base}@>(); // \expos
const Pred* @\exposid{pred_}@ = nullptr; // \expos
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end, const Pred* pred); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end, const Pred* pred);
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> s)
requires Const && @\libconcept{convertible_to}@<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -7152,11 +7151,11 @@
using @\exposid{Parent}@ = @\exposid{maybe-const}@<Const, join_view>; // \expos
using @\exposid{Base}@ = @\exposid{maybe-const}@<Const, V>; // \expos
sentinel_t<@\exposid{Base}@> @\exposid{end_}@ = sentinel_t<@\exposid{Base}@>(); // \expos
constexpr explicit @\exposid{sentinel}@(@\exposid{Parent}@& parent); // \expos

public:
@\exposid{sentinel}@() = default;

constexpr explicit @\exposid{sentinel}@(@\exposid{Parent}@& parent);
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> s)
requires Const && @\libconcept{convertible_to}@<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -7998,6 +7997,10 @@
// if \tcode{V} models \libconcept{forward_range}

bool @\exposid{trailing_empty_}@ = false; // \expos
constexpr explicit @\exposid{outer-iterator}@(@\exposid{Parent}@& parent) // \expos
requires (!@\libconcept{forward_range}@<@\exposid{Base}@>);
constexpr @\exposid{outer-iterator}@(@\exposid{Parent}@& parent, iterator_t<@\exposid{Base}@> current) // \expos
requires @\libconcept{forward_range}@<@\exposid{Base}@>;

public:
using iterator_concept =
Expand All @@ -8011,10 +8014,6 @@
using difference_type = range_difference_t<@\exposid{Base}@>;

@\exposid{outer-iterator}@() = default;
constexpr explicit @\exposid{outer-iterator}@(@\exposid{Parent}@& parent)
requires (!@\libconcept{forward_range}@<@\exposid{Base}@>);
constexpr @\exposid{outer-iterator}@(@\exposid{Parent}@& parent, iterator_t<@\exposid{Base}@> current)
requires @\libconcept{forward_range}@<@\exposid{Base}@>;
constexpr @\exposid{outer-iterator}@(@\exposid{outer-iterator}@<!Const> i)
requires Const && @\libconcept{convertible_to}@<iterator_t<V>, iterator_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -8232,9 +8231,10 @@
template<bool Const>
struct lazy_split_view<V, Pattern>::@\exposid{inner-iterator}@ {
private:
using @\exposidnc{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos
@\exposidnc{outer-iterator}@<Const> @\exposid{i_}@ = @\exposidnc{outer-iterator}@<Const>(); // \expos
bool @\exposid{incremented_}@ = false; // \expos
using @\exposidnc{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos
@\exposidnc{outer-iterator}@<Const> @\exposid{i_}@ = @\exposidnc{outer-iterator}@<Const>(); // \expos
bool @\exposid{incremented_}@ = false; // \expos
constexpr explicit @\exposid{inner-iterator}@(@\exposidnc{outer-iterator}@<Const> i); // \expos

public:
using iterator_concept = @\exposid{outer-iterator}@<Const>::iterator_concept;
Expand All @@ -8245,7 +8245,6 @@
using difference_type = range_difference_t<@\exposid{Base}@>;

@\exposid{inner-iterator}@() = default;
constexpr explicit @\exposid{inner-iterator}@(@\exposid{outer-iterator}@<Const> i);

constexpr const iterator_t<@\exposid{Base}@>& base() const & noexcept;
constexpr iterator_t<@\exposid{Base}@> base() && requires @\libconcept{forward_range}@<V>;
Expand Down Expand Up @@ -8556,10 +8555,12 @@
@\libconcept{indirectly_comparable}@<iterator_t<V>, iterator_t<Pattern>, ranges::equal_to>
class split_view<V, Pattern>::@\exposid{iterator}@ {
private:
split_view* @\exposid{parent_}@ = nullptr; // \expos
iterator_t<V> @\exposid{cur_}@ = iterator_t<V>(); // \expos
subrange<iterator_t<V>> @\exposid{next_}@ = subrange<iterator_t<V>>(); // \expos
bool @\exposid{trailing_empty_}@ = false; // \expos
split_view* @\exposid{parent_}@ = nullptr; // \expos
iterator_t<V> @\exposid{cur_}@ = iterator_t<V>(); // \expos
subrange<iterator_t<V>> @\exposid{next_}@ = subrange<iterator_t<V>>(); // \expos
bool @\exposid{trailing_empty_}@ = false; // \expos
constexpr @\exposid{iterator}@(split_view& parent, iterator_t<V> current, // \expos
subrange<iterator_t<V>> next);

public:
using iterator_concept = forward_iterator_tag;
Expand All @@ -8568,7 +8569,6 @@
using difference_type = range_difference_t<V>;

@\exposid{iterator}@() = default;
constexpr @\exposid{iterator}@(split_view& parent, iterator_t<V> current, subrange<iterator_t<V>> next);

constexpr iterator_t<V> base() const;
constexpr value_type operator*() const;
Expand Down Expand Up @@ -8683,10 +8683,10 @@
struct split_view<V, Pattern>::@\exposid{sentinel}@ {
private:
sentinel_t<V> @\exposid{end_}@ = sentinel_t<V>(); // \expos
constexpr explicit @\exposid{sentinel}@(split_view& parent); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(split_view& parent);

friend constexpr bool operator==(const @\exposid{iterator}@& x, const @\exposid{sentinel}@& y);
};
Expand Down Expand Up @@ -10322,6 +10322,7 @@
iterator_t<@\exposid{Base}@> @\exposid{current_}@ = iterator_t<@\exposid{Base}@>(); // \expos

static constexpr decltype(auto) @\exposid{get-element}@(const iterator_t<@\exposid{Base}@>& i); // \expos
constexpr explicit @\exposid{iterator}@(iterator_t<@\exposid{Base}@> current); // \expos

public:
using iterator_concept = @\seebelow@;
Expand All @@ -10330,7 +10331,6 @@
using difference_type = range_difference_t<@\exposid{Base}@>;

@\exposid{iterator}@() requires @\libconcept{default_initializable}@<iterator_t<@\exposid{Base}@>> = default;
constexpr explicit @\exposid{iterator}@(iterator_t<@\exposid{Base}@> current);
constexpr @\exposid{iterator}@(@\exposid{iterator}@<!Const> i)
requires Const && @\libconcept{convertible_to}@<iterator_t<V>, iterator_t<@\exposid{Base}@>>;

Expand Down Expand Up @@ -10717,12 +10717,12 @@
template<bool Const>
class elements_view<V, N>::@\exposid{sentinel}@ {
private:
using @\exposid{Base}@ = @\exposid{maybe-const}@<Const, V>; // \expos
using @\exposid{Base}@ = @\exposidnc{maybe-const}@<Const, V>; // \expos
sentinel_t<@\exposid{Base}@> @\exposid{end_}@ = sentinel_t<@\exposid{Base}@>(); // \expos
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end); // \expos

public:
@\exposid{sentinel}@() = default;
constexpr explicit @\exposid{sentinel}@(sentinel_t<@\exposid{Base}@> end);
constexpr @\exposid{sentinel}@(@\exposid{sentinel}@<!Const> other)
requires Const && @\libconcept{convertible_to}@<sentinel_t<V>, sentinel_t<@\exposid{Base}@>>;

Expand Down
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