std::ranges::ref_view - cppreference.com (original) (raw)
ref_view is a view of the elements of some other range. It wraps a reference to that range.
Contents
- 1 Data members
- 2 Member functions
- 3 std::ranges::ref_view::ref_view
- 4 std::ranges::ref_view::base
- 5 std::ranges::ref_view::begin
- 6 std::ranges::ref_view::end
- 7 std::ranges::ref_view::empty
- 8 std::ranges::ref_view::size
- 9 std::ranges::ref_view::reserve_hint
- 10 std::ranges::ref_view::data
[edit] Data members
| Member | Description |
|---|---|
| R* r_ | a pointer to the underlying range(exposition-only member object*) |
[edit] Member functions
| (constructor) | constructs a ref_view that references to the given range (public member function) |
|---|---|
| base | returns the references to the referenced range (public member function) |
| begin | returns the beginning iterator of the referenced range (public member function) |
| end | returns the sentinel of the referenced range (public member function) |
| empty | checks whether the referenced range is empty (public member function) |
| size | returns the size of the referenced sized_range (public member function) |
| reserve_hint(C++26) | returns the approximate size of the referenced approximately_sized_range (public member function) |
| data | returns the pointer to the beginning of the referenced contiguous_range (public member function) |
| Inherited from std::ranges::view_interface | |
| cbegin(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface) [edit] |
| cend(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface) [edit] |
| operator bool | returns whether the derived view is not empty, provided only if ranges::empty is applicable to it (public member function of std::ranges::view_interface) [edit] |
| front | returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface) [edit] |
| back | returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range (public member function of std::ranges::view_interface) [edit] |
| operator[] | returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface) [edit] |
std::ranges::ref_view::ref_view
| template< /*different-from*/<ref_view> T > requires std::convertible_to<T, R&> && requires { _FUN(std::declval<T>()); } constexpr ref_view( T&& t ); | | (since C++20) | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------- |
Initializes _[r](#r)_ with std::addressof(static_cast<R&>(std::forward<T>(t))).
/*different-from*/<T, U> is satisfied if and only if std::remove_cvref_t<T> and std::remove_cvref_t<U> are not the same type, and overloads of __FUN_ are declared as void _FUN(R&); void _FUN(R&&) = delete;.
Parameters
std::ranges::ref_view::base
| constexpr R& base() const; | | (since C++20) | | -------------------------- | | ------------- |
Returns *_[r](#r)_.
std::ranges::ref_view::empty
| constexpr bool empty() const requires requires { ranges::empty(*r_); }; | | (since C++20) | | -------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------- |
Returns ranges::empty(*_[r](#r)_ ).
std::ranges::ref_view::reserve_hint
| constexpr auto size() const requires ranges::approximately_sized_range<R>; | | (since C++26) | | ----------------------------------------------------------------------------- | | ------------- |
Returns ranges::reserve_hint(*_[r](#r)_ ).
[edit] Deduction guides
| template< class R >ref_view( R& ) -> ref_view<R>; | | (since C++20) | | ------------------------------------------------------- | | ------------- |
[edit] Helper templates
| template< class T > constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true; | | (since C++20) | | ------------------------------------------------------------------------------------------- | | ------------- |
This specialization of std::ranges::enable_borrowed_range makes ref_view satisfy borrowed_range.
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
| __cpp_lib_ranges_reserve_hint | 202502L | (C++26) | ranges::approximately_sized_range and reserve_hint |
[edit] Example
#include #include int main() { const std::string s{"cosmos"}; const std::ranges::take_view tv{s, 3}; const std::ranges::ref_view rv{tv}; std::cout << std::boolalpha << "call empty(): " << rv.empty() << '\n' << "call size() : " << rv.size() << '\n' << "call begin(): " << *rv.begin() << '\n' << "call end() : " << *(rv.end() - 1) << '\n' << "call data() : " << rv.data() << '\n' << "call base() : " << rv.base().size() << '\n' // ~> tv.size() << "range-for : "; for (const auto c : rv) std::cout << c; std::cout << '\n'; }
Output:
call empty(): false call size() : 3 call begin(): c call end() : s call data() : cosmos call base() : 3 range-for : cos
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2325R3 | C++20 | default constructor was provided asview must be default_initializable | removed along with the requirement |