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iota_view() requiresstd::default_initializable<W>=default; | (1) | (since C++20) |
constexprexplicit iota_view( W value); | (2) | (since C++20) |
constexprexplicit iota_view(std::type_identity_t<W> value, std::type_identity_t<Bound> bound); | (3) | (since C++20) |
constexprexplicit iota_view(/*iterator*/ first,/* see below */ last); | (4) | (since C++20) |
Constructs aniota_view.
| Overload | Data members | |
|---|---|---|
value_ | bound_ | |
| (1) | value-initialized | value-initialized |
| (2) | initialized withvalue | |
| (3) | initialized withbound | |
| (4) | initialized withfirst.value_ | see below |
Bound denotesstd::unreachable_sentinel_t.W andBound modeltotally_ordered_with, andbool(value<= bound) isfalse.Bound denotesstd::unreachable_sentinel_t.W andBound modeltotally_ordered_with, andbool(first.value_ <= bound) isfalse.bound_ are determined by the typeBound denotes:The typeBound denotes | The type oflast | bound_ |
|---|---|---|
W | iterator | initialized withlast.value_ |
| std::unreachable_sentinel_t | Bound | initialized withlast |
| any other type | sentinel | initialized withlast.bound_ |
| value | - | the starting value |
| bound | - | the bound |
| first | - | the iterator denoting the starting value |
| last | - | the iterator or sentinel denoting the bound |
#include <cassert>#include <iostream>#include <iterator>#include <ranges> int main(){constauto l={1,2,3,4}; auto i1= std::ranges::iota_view<int,int>();// overload (1)assert(i1.empty() and i1.size()==0); auto i2= std::ranges::iota_view(1);// overload (2)assert(not i2.empty() and i2.front()==1);for(std::cout<<"1) ";auto e: i2| std::views::take(3))std::cout<< e<<' ';std::cout<<'\n'; auto i3= std::ranges::iota_view(std::begin(l));// overload (2)assert(not i3.empty() and i3.front()== l.begin());for(std::cout<<"2) ";auto e: i3| std::views::take(4))std::cout<<*e<<' ';std::cout<<'\n'; auto i4= std::ranges::iota_view(1,8);// overload (3)assert(not i4.empty() and i4.front()==1 and i4.back()==7);for(std::cout<<"3) ";auto e: i4)std::cout<< e<<' ';std::cout<<'\n'; auto i5= std::ranges::iota_view(l.begin(), l.end());// overload (4)for(std::cout<<"4) ";auto e: i5)std::cout<<*e<<' ';std::cout<<'\n'; auto i6= std::ranges::iota_view(l.begin(),std::unreachable_sentinel);// (4)for(std::cout<<"5) ";auto e: i6| std::views::take(3))std::cout<<*e<<' ';std::cout<<'\n';}
Output:
1) 1 2 32) 1 2 3 43) 1 2 3 4 5 6 74) 1 2 3 45) 1 2 3
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3523 | C++20 | overload(4) might use wrong sentinel type | corrected |
| P2711R1 | C++20 | overloads(3,4) were not explicit | made explicit |
