[range.utility.conv.to] (original) (raw)

25 Ranges library [ranges]

25.5 Range utilities [range.utility]

25.5.7 Range conversions [range.utility.conv]

25.5.7.2 ranges​::​to [range.utility.conv.to]

template<class C, [input_range](range.refinements#concept:input%5Frange "25.4.5 Other range refinements [range.refinements]") R, class... Args> requires (![view](range.view#concept:view "25.4.4 Views [range.view]")<C>) constexpr C to(R&& r, Args&&... args);

Mandates: C is a cv-unqualified class type.

Returns: An object of type Cconstructed from the elements of r in the following manner:

• If C does not satisfy input_range orconvertible_to<range_reference_t<R>, range_value_t<C>>is true:
  • If constructible_from<C, R, Args...> is true:C(std::forward<R>(r), std::forward<Args>(args)...)
  • Otherwise, ifconstructible_from<C, from_range_t, R, Args...>is true:C(from_range, std::forward<R>(r), std::forward<Args>(args)...)
  • Otherwise, if
    * common_range<R> is true,
    * the qualified-id iterator_traits<iterator_t<R>>​::​iterator_categoryis valid and denotes a type that modelsderived_from<input_iterator_tag>, and
    * constructible_from<C, iterator_t<R>, sentinel_t<R>, Args...>is true:

  C(ranges::begin(r), ranges::end(r), std::forward<Args>(args)...)

  • Otherwise, if
    * constructible_from<C, Args...> is true, and
    * container-appendable<C, range_reference_t<R>> is true:

  C c(std::forward<Args>(args)...);if constexpr (approximately_sized_range<R> && reservable-container<C>) c.reserve(static_cast<range_size_t<C>>(ranges::reserve_hint(r))); ranges::for_each(r, container-append(c));

  • Otherwise, the program is ill-formed.
• Otherwise, if input_range<range_reference_t<R>> is true:to<C>(ref_view(r) | views::transform([](auto&& elem) { return to<range_value_t<C>>(std::forward<decltype(elem)>(elem));}), std::forward<Args>(args)...);
• Otherwise, the program is ill-formed.

template<template<class...> class C, [input_range](range.refinements#concept:input%5Frange "25.4.5 Other range refinements [range.refinements]") R, class... Args> constexpr auto to(R&& r, Args&&... args);

Let input-iterator be an exposition-only type:struct input-iterator { using iterator_category = input_iterator_tag;using value_type = range_value_t<R>;using difference_type = ptrdiff_t;using pointer = add_pointer_t<range_reference_t<R>>;using reference = range_reference_t<R>; reference operator*() const; pointer operator->() const;input-iterator& operator++();input-iterator operator++(int);bool operator==(const input-iterator&) const;};

[Note 1:

input-iterator meets the syntactic requirements of Cpp17InputIterator.

— _end note_]

Let DEDUCE_EXPR be defined as follows:

• C(declval<R>(), declval<Args>()...) if that is a valid expression,
• otherwise, C(from_range, declval<R>(), declval<Args>()...)if that is a valid expression,
• otherwise,C(declval<_input-iterator_>(), declval<_input-iterator_>(), declval<Args>()...) if that is a valid expression,
• otherwise, the program is ill-formed.

Returns: to<decltype(_DEDUCE_EXPR_)>(std​::​forward<R>(r), std​::​forward<Args>(args)...).