First cut of pulling out the relevant parts of my original game to make a little framework.

tests/dinkyecs.cpp

@@ -0,0 +1,212 @@
+#include <catch2/catch_test_macros.hpp>
+#include "algos/dinkyecs.hpp"
+#include <iostream>
+#include <fmt/core.h>
+
+using namespace fmt;
+using DinkyECS::Entity;
+using std::string;
+
+struct Point {
+  size_t x;
+  size_t y;
+};
+
+struct Player {
+  string name;
+  Entity eid;
+};
+
+struct Position {
+  Point location;
+};
+
+struct Motion {
+  int dx;
+  int dy;
+  bool random=false;
+};
+
+struct Velocity {
+  double x, y;
+};
+
+struct Gravity {
+  double level;
+};
+
+struct DaGUI {
+  int event;
+};
+
+/*
+ * Using a function catches instances where I'm not copying
+ * the data into the world.
+ */
+void configure(DinkyECS::World &world, Entity &test) {
+  println("---Configuring the base system.");
+  Entity test2 = world.entity();
+
+  world.set<Position>(test, {10,20});
+  world.set<Velocity>(test, {1,2});
+
+  world.set<Position>(test2, {1,1});
+  world.set<Velocity>(test2, {9,19});
+
+  println("---- Setting up the player as a fact in the system.");
+
+  auto player_eid = world.entity();
+  Player player_info{"Zed", player_eid};
+  // just set some player info as a fact with the entity id
+  world.set_the<Player>(player_info);
+
+  world.set<Velocity>(player_eid, {0,0});
+  world.set<Position>(player_eid, {0,0});
+
+  auto enemy = world.entity();
+  world.set<Velocity>(enemy, {0,0});
+  world.set<Position>(enemy, {0,0});
+
+  println("--- Creating facts (singletons)");
+  world.set_the<Gravity>({0.9});
+}
+
+TEST_CASE("confirm ECS system works", "[ecs]") {
+  DinkyECS::World world;
+  Entity test = world.entity();
+
+  configure(world, test);
+
+  Position &pos = world.get<Position>(test);
+  REQUIRE(pos.location.x == 10);
+  REQUIRE(pos.location.y == 20);
+
+  Velocity &vel = world.get<Velocity>(test);
+  REQUIRE(vel.x == 1);
+  REQUIRE(vel.y == 2);
+
+  world.query<Position>([](const auto &ent, auto &pos) {
+      REQUIRE(ent > 0);
+      REQUIRE(pos.location.x >= 0);
+      REQUIRE(pos.location.y >= 0);
+  });
+
+  world.query<Velocity>([](const auto &ent, auto &vel) {
+      REQUIRE(ent > 0);
+      REQUIRE(vel.x >= 0);
+      REQUIRE(vel.y >= 0);
+  });
+
+  println("--- Manually get the velocity in position system:");
+  world.query<Position>([&](const auto &ent, auto &pos) {
+      Velocity &vel = world.get<Velocity>(ent);
+
+      REQUIRE(ent > 0);
+      REQUIRE(pos.location.x >= 0);
+      REQUIRE(pos.location.y >= 0);
+      REQUIRE(ent > 0);
+      REQUIRE(vel.x >= 0);
+      REQUIRE(vel.y >= 0);
+  });
+
+  println("--- Query only entities with Position and Velocity:");
+  world.query<Position, Velocity>([&](const auto &ent, auto &pos, auto &vel) {
+      Gravity &grav = world.get_the<Gravity>();
+      REQUIRE(grav.level <= 1.0f);
+      REQUIRE(grav.level > 0.5f);
+      REQUIRE(ent > 0);
+      REQUIRE(pos.location.x >= 0);
+      REQUIRE(pos.location.y >= 0);
+      REQUIRE(ent > 0);
+      REQUIRE(vel.x >= 0);
+      REQUIRE(vel.y >= 0);
+  });
+
+  // now remove Velocity
+  REQUIRE(world.has<Velocity>(test));
+  world.remove<Velocity>(test);
+  REQUIRE_THROWS(world.get<Velocity>(test));
+  REQUIRE(!world.has<Velocity>(test));
+
+  println("--- After remove test, should only result in test2:");
+  world.query<Position, Velocity>([&](const auto &ent, auto &pos, auto &vel) {
+      auto &in_position = world.get<Position>(ent);
+      auto &in_velocity = world.get<Velocity>(ent);
+      REQUIRE(pos.location.x >= 0);
+      REQUIRE(pos.location.y >= 0);
+      REQUIRE(in_position.location.x == pos.location.x);
+      REQUIRE(in_position.location.y == pos.location.y);
+      REQUIRE(in_velocity.x == vel.x);
+      REQUIRE(in_velocity.y == vel.y);
+  });
+}
+
+enum GUIEvent {
+  HIT, MISS
+};
+
+TEST_CASE("confirm that the event system works", "[ecs]") {
+  DinkyECS::World world;
+  DinkyECS::Entity player = world.entity();
+
+  // this confirms we can send these in a for-loop and get them out
+  int i = 0;
+  for(; i < 10; i++) {
+    world.send<GUIEvent>(GUIEvent::HIT, player, string{"hello"});
+  }
+
+  // just count down and should get the same number
+  while(world.has_event<GUIEvent>()) {
+    auto [event, entity, data] = world.recv<GUIEvent>();
+    REQUIRE(event == GUIEvent::HIT);
+    REQUIRE(entity == player);
+    auto &str_data = std::any_cast<string&>(data);
+    REQUIRE(string{"hello"} == str_data);
+    i--;
+  }
+
+  REQUIRE(i == 0);
+}
+
+
+TEST_CASE("confirm copying and constants", "[ecs-constants]") {
+  DinkyECS::World world1;
+
+  Player player_info{"Zed", world1.entity()};
+  world1.set_the<Player>(player_info);
+
+  world1.set<Position>(player_info.eid, {10,10});
+  world1.make_constant(player_info.eid);
+
+  DinkyECS::World world2;
+  world1.clone_into(world2);
+
+  auto &test1 = world1.get<Position>(player_info.eid);
+  auto &test2 = world2.get<Position>(player_info.eid);
+
+  REQUIRE(test2.location.x == test1.location.x);
+  REQUIRE(test2.location.y == test1.location.y);
+
+  // check for accidental reference
+  test1.location.x = 100;
+  REQUIRE(test2.location.x != test1.location.x);
+
+  // test the facts copy over
+  auto &player2 = world2.get_the<Player>();
+  REQUIRE(player2.eid == player_info.eid);
+}
+
+TEST_CASE("can destroy all entity", "[ecs-destroy]") {
+  DinkyECS::World world;
+  auto entity = world.entity();
+
+  world.set<Velocity>(entity, {10,10});
+  world.set<Gravity>(entity, {1});
+  world.set<Motion>(entity, {0,0});
+
+  world.destroy(entity);
+
+  REQUIRE(!world.has<Velocity>(entity));
+  REQUIRE(!world.has<Gravity>(entity));
+  REQUIRE(!world.has<Motion>(entity));
+}