relationships/basics

• C

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  #include <basics.h>
  #include <stdio.h>
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      ECS_TAG(ecs, Eats);
   
      // Entity used for Grows relationship
      ecs_entity_t grows = ecs_entity(ecs, { .name = "Grows" });
   
      // Relationship objects
      ecs_entity_t apples = ecs_entity(ecs, { .name = "Apples" });
      ecs_entity_t pears = ecs_entity(ecs, { .name = "Pears" });
   
      // Create an entity with 3 relationships. Relationships are like regular components,
      // but combine two types/identifiers into an (relationship, object) pair.
      ecs_entity_t bob = ecs_entity(ecs, { .name = "Bob" });
      // Pairs can be constructed from a type and entity
      ecs_add_pair(ecs, bob, Eats, apples);
      ecs_add_pair(ecs, bob, Eats, pears);
      // Pairs can also be constructed from two entity ids
      ecs_add_pair(ecs, bob, grows, pears);
   
      // Has can be used with relationships as well
      printf("Bob eats apples? %d\n", ecs_has_pair(ecs, bob, Eats, apples));
   
      // Wildcards can be used to match relationships
      printf("Bob grows food? %d\n", ecs_has_pair(ecs, bob, grows, EcsWildcard));
   
      // Print the type of the entity. Should output:
      //   (Identifier,Name),(Eats,Apples),(Eats,Pears),(Grows,Pears)
      char *type_str = ecs_type_str(ecs, ecs_get_type(ecs, bob));
      printf("Bob's type: [%s]\n", type_str);
      ecs_os_free(type_str);
   
      // Get first target of relationship
      printf("Bob eats %s\n", 
          ecs_get_name(ecs, ecs_get_target(ecs, bob, Eats, 0)));
   
      // Get second target of relationship
      printf("Bob also eats %s\n", 
          ecs_get_name(ecs, ecs_get_target(ecs, bob, Eats, 1)));
   
      return ecs_fini(ecs);
  }

• C++

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  #include <basics.h>
  #include <iostream>
   
  // Type used for Eats relationship
  struct Eats { };
   
  int main(int, char*[]) {
      flecs::world ecs;
   
      // Entity used for Grows relationship
      flecs::entity grows = ecs.entity("Grows");
   
      // Relationship objects
      flecs::entity apples = ecs.entity("Apples");
      flecs::entity pears = ecs.entity("Pears");
   
      // Create an entity with 3 relationships. Relationships are like regular components,
      // but combine two types/identifiers into an (relationship, object) pair.
      flecs::entity bob = ecs.entity("Bob")
          // Pairs can be constructed from a type and entity
          .add<Eats>(apples)
          .add<Eats>(pears)
          // Pairs can also be constructed from two entity ids
          .add(grows, pears);
   
      // Has can be used with relationships as well
      std::cout << "Bob eats apples? " << bob.has<Eats>(apples) << "\n";
   
      // Wildcards can be used to match relationships
      std::cout << "Bob grows food? " << bob.has(grows, flecs::Wildcard) << "\n";
   
      // Print the type of the entity. Should output:
      //   (Identifier,Name),(Eats,Apples),(Eats,Pears),(Grows,Pears)
      std::cout << "Bob's type: [" << bob.type().str() << "]\n";
   
      // Relationships can be iterated for an entity. This iterates (Eats, *):
      bob.each<Eats>([](flecs::entity second) {
          std::cout << "Bob eats " << second.name() << "\n";
      });
   
      // Iterate by explicitly providing the pair. This iterates (*, Pears):
      bob.each(flecs::Wildcard, pears, [](flecs::id id) {
          std::cout << "Bob " << id.first().name() << " pears\n";
      });
   
      // Get first target of relationship
      std::cout << "Bob eats " << bob.target<Eats>().name() << "\n";
   
      // Get second target of relationship
      std::cout << "Bob also eats " << bob.target<Eats>(1).name() << "\n";
  }