relationships/enum_relations

• C++

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  #include <enum_relations.h>
  #include <stdio.h>
   
  // When an enumeration constant is added to an entity, it is added as a relationship
  // pair where the relationship is the enum type, and the target is the constant. For
  // example, this statement:
  //   e.add(Color::Red)
  //
  // adds this relationship:
  //   (Color, Color::Red)
  //
  // Enums are registered as exclusive relationships, which means that adding an
  // enum constant will replace the previous constant for that enumeration:
  //   e.add(Color::Green)
  //
  //  will replace Color::Red with Color::Green
   
  // Regular enumerations are supported
  enum Tile {
      Grass, 
      Sand, 
      Stone
  };
   
  // Enum classes are supported
  enum class TileStatus {
      Free,
      Occupied,
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create an entity with (Tile, Stone) and (TileStatus, Free) relationships
      flecs::entity tile = ecs.entity()
          .add(Tile::Stone)
          .add(TileStatus::Free);
   
      // (Tile, Tile.Stone), (TileStatus, TileStatus.Free)
      printf("%s\n", tile.type().str().c_str());
   
      // Replace (TileStatus, Free) with (TileStatus, Occupied)
      tile.add(TileStatus::Occupied);
   
      // (Tile, Tile.Stone), (TileStatus, TileStatus.Occupied)
      printf("%s\n", tile.type().str().c_str());
   
      // Check if the entity has the Tile relationship and the Tile::Stone pair
      printf("%s\n", tile.has<Tile>() ? "true" : "false"); // true
      printf("%s\n", tile.has(Tile::Stone) ? "true" : "false"); // true
   
      // Get the current value of the enum
      Tile v = tile.get_constant<Tile>();
      printf("%s\n", (v == Tile::Stone) ? "true" : "false"); // true
   
      // Create a few more entities that we can query
      ecs.entity().add(Tile::Grass).add(TileStatus::Free);
      ecs.entity().add(Tile::Sand).add(TileStatus::Occupied);
   
      // Iterate all entities with a Tile relationship
      ecs.query_builder()
          .with<Tile>(flecs::Wildcard)
          .build()
          .each([&](flecs::iter& it, size_t) {
              flecs::entity tile_constant = it.pair(0).second();
              printf("%s\n", tile_constant.path().c_str());
          });
   
      // Outputs:
      //  ::Tile::Stone
      //  ::Tile::Grass
      //  ::Tile::Sand
   
      // Iterate only occupied tiles
      ecs.query_builder()
          .with<Tile>(flecs::Wildcard)
          .with(TileStatus::Occupied)
          .build()
          .each([&](flecs::iter& it, size_t) {
              flecs::entity tile_constant = it.pair(0).second();
              printf("%s\n", tile_constant.path().c_str());
          });
   
      // Outputs:
      //  ::Tile::Stone
      //  ::Tile::Sand
   
      // Remove any instance of the TileStatus relationship
      tile.remove<TileStatus>(flecs::Wildcard);
  }