C++ 中文周刊 第82期

struct s {
  static constexpr auto operator()() { return 1; }
};
auto l = [] static { return 2; };

static_assert(3 == s{}() + l());

static_assert(3 == s::operator()() +
         decltype(l)::operator()());

for (int i = 0; i < ssize(vec); ++i)
    std::cout << i << ": " << vec[i] << '\n';

int main() {
    std::vector vec { 1, 2, 3, 4, 5};
    for (int i = 0; const auto& elem : vec)
        std::cout << i++ << ": " << elem << '\n';
}

#include <iostream>
#include <vector>
#include <ranges>

int main() {
    std::vector vec { 1, 2, 3, 4, 5};
    for (int i = 0; const auto& elem : vec | std::views::reverse)
        std::cout << i++ << ": " << elem << '\n';
}

void printReverse(auto cont) {
    std::ranges::for_each(cont | std::views::reverse, 
        [i=0](const auto& elem) mutable {
            std::cout << i++ << ' ' << elem << '\n';
        }
    );
}

    const char * str1 = "dear friend";
    const char * str2 = "dear friend";
    return str1 == str2;

void oops(std::vector<std::string>& v)
{
    set_name(v.front.c_str());
    //         ^^^^^ error: A pointer to a bound function
    //         may only be used to call the function
}

class animal_view {
 public:
  template <typename Speakable>
  explicit animal_view(const Speakable &speakable)
      : object{&speakable},
        speak_impl{// create a lambda that knows how to unpack the stored object
                   [](const void *obj) {
                     return static_cast<const Speakable *>(obj)->speak();
                   }} {}

  void speak() const { speak_impl(object); }

 private:
  // void * to object of unknown type
  const void *object;

  // function pointer that knows how to use unknown type
  void (*speak_impl)(const void *);
};

void do_animal_things(animal_view animal) { animal.speak(); }

int main() {
  struct Cow {
    void speak() const { fmt::print("Mooo\n"); }
  };

  struct Sheep {
    void speak() const { fmt::print("Baaa\n"); }
  };
  do_animal_things(animal_view{Cow{}});
  do_animal_things(animal_view{Sheep{}});
}

     This site is open source. [Improve this page](https://github.com/wanghenshui/cppweeklynews/edit/dev/posts/082.md).