queries/each_w_entity_callback

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  #include <each_w_entity_callback.h>
  #include <iostream>
   
  // This example is the same as the each example, but in addition also shows how 
  // to get access to the matched entity.
   
  struct Position { 
      double x, y;
  };
   
  struct Velocity { 
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create a query for Position, Velocity.
      flecs::query<Position, const Velocity> q = 
          ecs.query<Position, const Velocity>();
   
      // Create a few test entities for a Position, Velocity query
      ecs.entity("e1")
          .set<Position>({10, 20})
          .set<Velocity>({1, 2});
   
      ecs.entity("e2")
          .set<Position>({10, 20})
          .set<Velocity>({3, 4});
   
      // This entity will not match as it does not have Position, Velocity
      ecs.entity("e3")
          .set<Position>({10, 20});
   
      // Arguments passed to each match components passed to system
      q.each([](flecs::entity e, Position& p, const Velocity& v) {
          p.x += v.x;
          p.y += v.y;
          std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
      });
   
      // Output
      //  e1: {11, 22}
      //  e2: {13, 24}
  }