| ||||||||||||||||||||||
| Range primitives | |||||||
| |||||||
| Range concepts | |||||||||||||||||||
| |||||||||||||||||||
| Range factories | |||||||||
| |||||||||
| Range adaptors | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Helper items | |||||||||||||||||
| |||||||||||||||||
| Member functions | ||||
transform_view::transform_view | ||||
(C++26) | ||||
| Deduction guides | ||||
| Iterator | ||||
| Sentinel | ||||
transform_view() requiresstd::default_initializable<V>&& std::default_initializable<F>=default; | (1) | (since C++20) |
constexprexplicit transform_view( V base, F fun); | (2) | (since C++20) |
Constructs atransform_view.
base_ and the transformation functionfun_.| base | - | view |
| fun | - | transformation function |
Demonstratesπ approximation using serial expansion of arc tangent of1:atan(1) = π/4 ≈ 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...
#include <algorithm>#include <functional>#include <iomanip>#include <iostream>#include <numeric>#include <ranges> int main(){std::cout<<std::setprecision(15)<<std::fixed;auto atan1term{std::ranges::views::transform([](int n){return((n%2)?-1:1)*1.0/(2* n+1);})};for(constint iterations:{1,2,3,4,5,10,100,1000,1'000'000}){auto seq{std::ranges::views::iota(0, iterations) bitor atan1term};constdouble accum{*std::ranges::fold_left_first(seq,std::plus{})};std::cout<<"π ≈ "<<4* accum<<" (iterations: "<< iterations<<")\n";}std::cout<<"π ≈ "<<std::numbers::pi<<" (std::numbers::pi)\n";}
Possible output:
π ≈ 4.000000000000000 (iterations: 1)π ≈ 2.666666666666667 (iterations: 2)π ≈ 3.466666666666667 (iterations: 3)π ≈ 2.895238095238096 (iterations: 4)π ≈ 3.339682539682540 (iterations: 5)π ≈ 3.041839618929403 (iterations: 10)π ≈ 3.131592903558554 (iterations: 100)π ≈ 3.140592653839794 (iterations: 1000)π ≈ 3.141591653589774 (iterations: 1000000)π ≈ 3.141592653589793 (std::numbers::pi)
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3714 (P2711R1) | C++20 | the multi-parameter constructor was not explicit | made explicit |
| P2325R3 | C++20 | ifF is notdefault_initializable, the default constructorconstructs a transform_view which does not contain anF | thetransform_view is alsonot default_initializable |
