reflection/ser_std_optional

• C++

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  #include <ser_std_optional.h>
  #include <iostream>
  #include <optional>
   
  template <typename T>
  flecs::opaque<std::optional<T>, T> std_optional_support(flecs::world &world) {
    return flecs::opaque<std::optional<T>, T>()
        .as_type(world.vector<T>())
        .serialize([](const flecs::serializer *s, const std::optional<T> *data) {
          if (*data) {
            s->value(**data);
          }
          return 0;
        })
        .count(
            [](const std::optional<T> *data) -> size_t { return *data ? 1 : 0; })
        .resize([](std::optional<T> *data, size_t size) {
          switch (size) {
          case 0:
            *data = std::nullopt;
            break;
          case 1:
            if (!data->has_value()) {
              *data = T();
            }
            break;
          default:
            assert(false);
          }
        })
        .ensure_element([](std::optional<T> *data, size_t) {
          if (!data->has_value()) {
            *data = T();
          }
          return &data->value();
        });
  }
   
  int main(int, char *[]) {
    flecs::world ecs;
   
    // Register reflection for std::optional<int>
    ecs.component<std::optional<int>>()
      .opaque(std_optional_support<int>);
   
    std::optional<int> empty = std::nullopt;
    std::cout << ecs.to_json(&empty) << std::endl;
   
    std::optional<int> full = 1;
    std::cout << ecs.to_json(&full) << std::endl;
   
    std::optional<int> o;
    ecs.from_json(&o, "[2]");
    std::cout << ecs.to_json(&o) << std::endl;
   
    // Output:
    //   []
    //   [1]
    //   [2]
  }