entities/get_n

• C++

  View on GitHub

  #include <get_n.h>
  #include <iostream>
   
  /* This code shows how to get multiple components in a single command */
   
  struct Position {
      double x, y;
  };
   
  struct Mass {
      double value;
  };
   
  struct Velocity {
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create new entity, set Position and Mass component
      flecs::entity e = ecs.entity()
          .insert([](Position& p, Mass& m) {
              p.x = 10;
              p.y = 20;
              m.value = 100;
          });
   
      {
          auto [pos, mass] = e.get_mut_n<Position, Mass>();
          pos.x += 5;
          mass.value += 3;
          std::cout << "Position: {" << pos.x << ", " << pos.y << "}\n";
          std::cout << "Mass: {" << mass.value << "}\n";
          // Output:
          //  Position: {15, 20}
          //  Mass: {103}
      }
      std::cout << "\n";
      {
          const auto [pos, mass] = e.get_n<Position, Mass>();
          // pos.x += 5; // Will not compile here!
          // mass.value += 3; // Will not compile here!
          std::cout << "Position: {" << pos.x << ", " << pos.y << "}\n";
          std::cout << "Mass: {" << mass.value << "}\n";
          // Output:
          //  Position: {15, 20}
          //  Mass: {100}
      }
      std::cout << "\n";
      // It's possible to try_get_n with absent component that will return null
      {
          const auto [pos, velocity, mass] = e.try_get_n<Position, Velocity, Mass>();
   
          std::cout << "Position: {" << pos->x << ", " << pos->y << "}\n";
          if (velocity) {
              std::cout << "Velocity: {" << velocity->x << ", " << velocity->y << "}\n";
          } else {
              std::cout << "Velocity: not found\n";
          }
          std::cout << "Mass: {" << mass->value << "}\n";
          // Output:
          //  Position: {15, 20}
          //  Velocity: not found
          //  Mass: {100}
      }
      
      return 0;
  }