C++ 动态新闻推送 第61期

#define FWD(...) static_cast<decltype(__VA_ARGS__)&&>(__VA_ARGS__)

[[nodiscard]] constexpr auto bind_back(const auto& func, auto... bound_args) {
    return [=] [[nodiscard]] (auto&&... unbound_args) {
        return func(FWD(unbound_args)..., bound_args...);
    };
}

int main() {
  //std::cout << std::bind_front(std::divides{}, 2.)(1.); // prints 2
  std::cout << std::bind_back (std::divides{}, 2.)(1.); // prints 0.5
}

#include <algorithm>
#include <vector>
#include <iostream>
#include <ranges>   // new header!

int main() {
    const std::vector numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    auto even = [](int i) { return 0 == i % 2; };
 
    std::ranges::reverse_view rv{ 
        std::ranges::drop_view { 
            std::ranges::filter_view{ numbers, even }, 1 
        }
    };
    for (auto& i : rv)
        std::cout << i << ' ';;                                 
}

#include <iostream>
#include <type_traits>

class A {
  int a;
  int b;
};


class C {
  C (int& ib) : b(ib) {}
  int a;
  int& b;
};


int main() {
  std::cout << std::boolalpha;
  std::cout << std::is_standard_layout_v<A> << '\n';
  std::cout << std::is_standard_layout_v<C> << '\n';
}

template<typename T>
constexpr T winrt_empty_value() noexcept
{
    if constexpr (std::is_base_of_v<winrt::Windows::Foundation::IUnknown, T>) {
        return nullptr;
    } else {
        return {};
    }
}

struct S;
const S foo(); // bad

struct S;
S foo() {
  const S s1;
  const S s2;
  if (/*some condition */) {
  	return s1;
  } else {
  	return s2;
  }
}

struct S;
S foo(const S s) {
	// do sth with s
  return s;
}

struct S {
 const int a;
}

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