Difference between revisions of "cpp/ranges/ref view"
m (→Helper templates: ~) |
(+ example) |
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===Example=== | ===Example=== | ||
| − | {{example}} | + | {{example|code= |
| + | #include <ranges> | ||
| + | #include <iostream> | ||
| + | |||
| + | 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 | ||
| + | }} | ||
===See also=== | ===See also=== | ||
Revision as of 10:22, 11 September 2020
| Defined in header <ranges>
|
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| template<ranges::range R> requires std::is_object_v<R> |
(since C++20) | |
ref_view is a view of the elements of some other range. It wraps a reference to that range.
Contents |
Helper templates
| template<class T> inline constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true; |
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This specialization of std::ranges::enable_borrowed_range makes ref_view satisfy borrowed_range.
Data members
std::ranges::ref_view::r_
| R* r_ = nullptr; /* exposition-only */ |
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pointer to the referenced range
Member functions
std::ranges::ref_view::ref_view
| constexpr ref_view() noexcept = default; |
(1) | |
| template<__NotSameAs<ref_view> T> requires std::convertible_to<T, R&> && requires { _FUN(std::declval<T>()); } |
(2) | |
Names __NotSameAs and _FUN are exposition-only. __NotSameAs<T, U> is satisfied if and only if !std::same_as<std::remove_cvref_t<T>, std::remove_cvref_t<U>>. The function _FUN are declared as void _FUN(R&); void _FUN(R&&) = delete;.
Parameters
| t | - | range to reference |
std::ranges::ref_view::base
| constexpr R& base() const; |
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Equivalent to return *r_;
std::ranges::ref_view::begin
| constexpr ranges::iterator_t<R> begin() const; |
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Equivalent to return ranges::begin(*r_);
std::ranges::ref_view::end
| constexpr ranges::sentinel_t<R> end() const; |
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Equivalent to return ranges::end(*r_);
std::ranges::ref_view::empty
| constexpr bool empty() const requires requires { ranges::empty(*r_); }; |
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Equivalent to return ranges::empty(*r_);
std::ranges::ref_view::size
| constexpr auto size() const requires ranges::sized_range<R> |
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std::ranges::ref_view::data
| constexpr auto data() const requires ranges::contiguous_range<R> |
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Deduction guides
| template<class R> ref_view(R&) -> ref_view<R>; |
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Example
#include <ranges> #include <iostream> 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
See also
| (C++11) |
CopyConstructible and CopyAssignable reference wrapper (class template) |
| (C++20) |
a view that includes all elements of a range(alias template) (range adaptor object) |
