UnityECS/LocalPackages/com.nimin.tinyecs/Runtime/EntityDatabase.cs

using System;
using Unity.Collections;
using Unity.Mathematics;

namespace GameCore.TinyECS
{
    public struct EntityDatabase<TEnum, TData> : IDisposable where TEnum : unmanaged where TData : unmanaged, IEntityDataStruct
    {
        public TData dataStruct;
        public EntityGenerator<TEnum> generator;
        public EntityCollection<TEnum> collection;

        public Entity<TEnum> AddEntity()
        {
            var entity = generator.Create();
            collection.Add(entity);
            dataStruct.Add();
            return entity;
        }

        public void RemoveEntity(Entity<TEnum> entity)
        {
            generator.Delete(entity);
            if (collection.Remove(entity, out var index, out var _))
                dataStruct.Remove(index);
        }

        public void Dispose()
        {
            generator.Dispose();
            collection.Dispose();
            dataStruct.Dispose();
        }
    }
}