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std::ranges...ansform_view(3) C++ Standard Libarystd::ranges...ansform_view(3) NAME std::ranges::transform_view::transform_view - std::ranges::trans- form_view::transform_view Synopsis transform_view() requires std::default_initializable<V> && (1) (since C++20) std::default_initializable<F> = default; constexpr explicit transform_view( V base, F fun ); (2) (since C++20) Constructs a transform_view. 1) Default constructor. Value-initializes the underlying view and the transformation function. 2) Move constructs the underlying view from base and the transforma- tion function from fun. Parameters base - view fun - transformation function Example Demonstrates approximation using serial expansion of arc tangent of 1: atan(1) = /4 ~ 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ... // Run this code #include <iomanip> #include <iostream> #include <numbers> #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 (const int iterations : {1, 2, 3, 4, 5, 10, 100, 1000, 1'000'000}) { auto seq = std::ranges::views::iota(0, iterations) | atan1term; const double accum = std::accumulate(seq.begin(), seq.end(), 0.0); std::cout << " ~ " << 4 * accum << " (iterations: " << itera- tions << ")\n"; } std::cout << " ~ " << std::numbers::pi << " (std::numbers::pi)\n"; } Possible output: ~ 4.000000000000000 (iterations: 1) ~ 2.666666666666667 (iterations: 2) ~ 3.466666666666667 (iterations: 3) ~ 2.895238095238096 (iterations: 4) ~ 3.339682539682540 (iterations: 5) ~ 3.041839618929403 (iterations: 10) ~ 3.131592903558554 (iterations: 100) ~ 3.140592653839794 (iterations: 1000) ~ 3.141591653589774 (iterations: 1000000) ~ 3.141592653589793 (std::numbers::pi) Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior LWG 3714 C++20 the multi-parameter constructor was made ex- plicit (P2711R1) not explicit if F is not default_initializable, P2325R3 C++20 the default constructor the trans- form_view is also constructs a transform_view which not de- fault_initializable does not contain an F http://cppreference.com 2024.06.10 std::ranges...ansform_view(3)
NAME | Synopsis | Parameters | Example | Possible output:
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