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Defined in header <ranges> | ||
| (1) | ||
template<std::copy_constructible T> requiresstd::is_object_v<T> | (since C++20) (until C++23) | |
template<std::move_constructible T> requiresstd::is_object_v<T> | (since C++23) | |
namespace views{ inlineconstexpr/* unspecified */ single=/* unspecified */; | (2) | (since C++20) |
Call signature | ||
template<class T> requires/* see below */ | (since C++20) | |
view that contains exactly one element of a specified value.The lifetime of the element is bound to the parentsingle_view. Copyingsingle_view makes a copy of the element.
Contents |
The nameviews::single denotes acustomization point object, which is a constfunction object of aliteralsemiregular class type. SeeCustomizationPointObject for details.
| Member | Definition |
copyable-box <T>value_(until C++23) | the single element of the view (exposition-only member object*) |
movable-box <T>value_(since C++23) | the single element of the view (exposition-only member object*) |
constructs asingle_view(public member function) | |
| returns a pointer to the element (public member function) | |
| returns a pointer past the element (public member function) | |
[static] | returnsfalse (public static member function) |
[static] | returns1 (public static member function) |
| returns a pointer to the element (public member function) | |
Inherited fromstd::ranges::view_interface | |
(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface<D>)[edit] |
(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface<D>)[edit] |
| returns whether the derived view is not empty, provided only ifranges::empty is applicable to it (public member function of std::ranges::view_interface<D>)[edit] | |
returns the first element in the derived view, provided if it satisfiesforward_range(public member function of std::ranges::view_interface<D>)[edit] | |
returns the last element in the derived view, provided only if it satisfiesbidirectional_range andcommon_range(public member function of std::ranges::view_interface<D>)[edit] | |
returns thenth element in the derived view, provided only if it satisfiesrandom_access_range(public member function of std::ranges::view_interface<D>)[edit] | |
single_view() requiresstd::default_initializable<T>=default; | (1) | (since C++20) |
| (2) | ||
constexprexplicit single_view(const T& t); | (since C++20) (until C++23) | |
constexprexplicit single_view(const T& t) requiresstd::copy_constructible<T>; | (since C++23) | |
constexprexplicit single_view( T&& t); | (3) | (since C++20) |
template<class...Args> requiresstd::constructible_from<T, Args...> | (4) | (since C++20) |
Constructs asingle_view.
value_, which value-initializes its contained value.value_ witht.value_ withstd::move(t).constexpr T* begin()noexcept; constexprconst T* begin()constnoexcept; | (since C++20) | |
Equivalent toreturn data();.
constexpr T* end()noexcept; constexprconst T* end()constnoexcept; | (since C++20) | |
Equivalent toreturn data()+1;.
staticconstexprbool empty()noexcept; | (since C++20) | |
Equivalent toreturnfalse;.
staticconstexprstd::size_t size()noexcept; | (since C++20) | |
Equivalent toreturn1;.
Makessingle_view model/*tiny-range*/ as required bysplit_view.
constexpr T* data()noexcept; constexprconst T* data()constnoexcept; | (since C++20) | |
Returns a pointer to the contained value ofvalue_. The behavior is undefined ifvalue_ does not contains a value.
template<class T> single_view( T)-> single_view<T>; | (since C++20) | |
For asingle_view, the inheritedempty member function always returnsfalse, and the inheritedoperatorbool conversion function always returnstrue.
#include <iomanip>#include <iostream>#include <ranges>#include <string>#include <tuple> int main(){constexpr std::ranges::single_view sv1{3.1415};// uses (const T&) constructor static_assert(sv1); static_assert(not sv1.empty()); std::cout<<"1) *sv1.data(): "<<*sv1.data()<<'\n'<<"2) *sv1.begin(): "<<*sv1.begin()<<'\n'<<"3) sv1.size(): "<< sv1.size()<<'\n'<<"4) distance: "<<std::distance(sv1.begin(), sv1.end())<<'\n'; std::string str{"C++20"};std::cout<<"5) str = "<<std::quoted(str)<<'\n'; std::ranges::single_view sv2{std::move(str)};// uses (T&&) constructorstd::cout<<"6) *sv2.data(): "<<std::quoted(*sv2.data())<<'\n'<<"7) str = "<<std::quoted(str)<<'\n'; std::ranges::single_view<std::tuple<int,double,std::string>> sv3{std::in_place,42,3.14,"😄"};// uses (std::in_place_t, Args&&... args) std::cout<<"8) sv3 holds a tuple: { "<< std::get<0>(sv3[0])<<", "<< std::get<1>(sv3[0])<<", "<< std::get<2>(sv3[0])<<" }\n";}
Output:
1) *sv1.data(): 3.14152) *sv1.begin(): 3.14153) sv1.size(): 14) distance: 15) str = "C++20"6) *sv2.data(): "C++20"7) str = ""8) sv3 holds a tuple: { 42, 3.14, 😄 }The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3428 | C++20 | single_view was convertible fromstd::in_place_t | the constructor is made explicit |
| LWG 4035 | C++20 | single_view did not provide the member functionempty() | providesempty() |
| P2367R0 | C++20 | deduction guides forsingle_view failed to decay the argument;views::single copied but not wrapped asingle_view | a decaying guide provided; made always wrapping |
(C++17) | a wrapper that may or may not hold an object (class template)[edit] |
an emptyview with no elements(class template)(variable template)[edit] | |
aview over the subranges obtained from splitting anotherview using a delimiter(class template)(range adaptor object)[edit] |
