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Defined in header <ranges> | ||
template<class R> using values_view=ranges::elements_view<R,1>; | (1) | (since C++20) |
namespace views{ inlineconstexprauto values= ranges::elements<1>; | (2) | (since C++20) |
Takes aview oftuple-like values (e.g.std::tuple orstd::pair), and produces a view with avalue-type of thesecond element of the adapted view's value-type.
Contents |
values_view can be useful for extractingvalues from associative containers, e.g.
std::map<int,std::string> map{{1,"alpha"},{2,"beta"}};for(autoconst& value: std::views::values(map))std::cout<< value<<' ';// prints: alpha beta
#include <iostream>#include <map>#include <ranges> int main(){constauto list={std::pair{1,11.1},{2,22.2},{3,33.3}};std::cout<<"pair::second values in the list: ";for(double value: list| std::views::values)std::cout<< value<<' '; std::map<char,int> map{{'A',1},{'B',2},{'C',3},{'D',4},{'E',5}};auto odd=[](int x){return0!=(x&1);};std::cout<<"\nodd values in the map: ";for(int value: map| std::views::values| std::views::filter(odd))std::cout<< value<<' ';std::cout<<'\n';}
Output:
pair::second values in the list: 11.1 22.2 33.3odd values in the map: 1 3 5
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3563 | C++20 | keys_view is unable to participate in CTAD due to its use ofviews::all_t | views::all_t removed |
(C++20) | takes aview consisting of pair-like values and produces aview of the first elements of each pair(class template)(range adaptor object)[edit] |
takes aview consisting oftuple-like values and a number N and produces aview of Nth element of each tuple(class template)(range adaptor object)[edit] | |
| BLAS-like slice of a valarray: starting index, length, stride (class)[edit] |
