c++17 代码你能看懂吗?

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 #include <vector>
 #include <algorithm>
 #include <random>
 
 int main()
 {
     std::vector<int> a{, , , , , , , , , , };
     std::vector<int> b();
 
     std::sample(a.begin(), a.end(),
                 b.begin(), b.size(),
                 std::mt19937{std::random_device{}()});
     return ;
 }
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 #include <iostream>
 #include <string>
 
 int main()
 {
     const std::string myString = "Hello World";
 
     // C++17 with init if:
     if (const auto it = myString.find("Hello"); it != std::string::npos)
         std::cout << it << " Hello\n";
 
     if (const auto it = myString.find("World"); it != std::string::npos)
         std::cout << it << " World\n";
 }
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 #include <iostream>
 #include <string>
 
 using namespace std;
 
 template<typename ...Args> auto sum(Args ...args)
 {
     return (args + ... + );
 }
 
 template<typename ...Args> auto sum2(Args ...args)
 {
     return (args + ...);
 }
 
 int main()
 {
     cout << sum(, , , , , , ) << "\n";
     cout << sum2(, , , , , , ) << "\n";
 }
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 #include <utility>
 #include <tuple>
 #include <iostream>
 
 int main() {
     std::pair d(, 0.0);
     std::tuple t(, , );
 
     std::cout << std::get<>(t) << ", " << std::get<>(t) << ", " << std::get<>(t) << "\n";
 }
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 #include <iostream>
 #include <string>
 
 struct S
 {
     int n;
     std::string s;
     float d;
 };
 
 template <std::size_t I>
 auto& get(S& s)
 {
     if constexpr (I == )
         return s.n;
     else if constexpr (I == )
         return s.s;
     else if constexpr (I == )
         return s.d;
 }
 
 int main()
 {
     S obj { , "hello", 10.0f };
     std::cout << get<>(obj) << ", " << get<>(obj) << "\n";
 }
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 https://www.codingame.com/playgrounds/2205/7-features-of-c17-that-will-simplify-your-code/introduction
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