EntityDiff.cs

public static class EntityDiff
{
    public static ComponentDiffResult<T1> Diff<T1, T2>(this Entity entity, World world = null)
        where T1: struct, IComponentData, IEquatable<T1>
        where T2: struct, IDiffComponent<T1>
    {
        if (world == null)
        {
            world = World.Active;
        }

        var hasCurrent = entity.HasComponent<T1>(world);
        var hasOld = entity.HasComponent<T2>(world);

        if (hasCurrent == false && hasOld == false)
        {
            return new ComponentDiffResult<T1>
            {
                Type = ChangeType.NotPresent
            };
        }
        
        if (hasCurrent && hasOld == false)
        {
            var component = entity.GetComponentData<T1>(world);
            return new ComponentDiffResult<T1>
            {
                Type = ChangeType.Added,
                Old = component,
                Current = component
            };
        }

        if (hasCurrent == false)
        {
            var component = entity.GetComponentData<T2>(world).Value;
            return new ComponentDiffResult<T1>
            {
                Type = ChangeType.Removed,
                Old = component,
                Current = component
            };
        }

        var before = entity.GetComponentData<T2>(world).Value;
        var after = entity.GetComponentData<T1>(world);
        if (before.Equals(after))
        {
            return new ComponentDiffResult<T1>
            {
                Type = ChangeType.NothingChanged,
                Old = before,
                Current = after
            };
        }
        return new ComponentDiffResult<T1>
        {
            Type = ChangeType.Updated,
            Old = before,
            Current = after
        };
    }

    public static ComponentDiffResult<T1> Balance<T1, T2>(this Entity entity, World world = null)
        where T1 : struct, IComponentData, IEquatable<T1>
        where T2 : struct, IDiffComponent<T1>
    {
        if (world == null)
        {
            world = World.Active;
        }

        var diffResult = entity.Diff<T1, T2>();
        switch (diffResult.Type)
        {
            case ChangeType.Added:
            case ChangeType.Updated:
                entity.AddComponentData(new T2{Value = diffResult.Current});
                break;
            case ChangeType.Removed:
                entity.RemoveComponent<T2>();
                break;
            case ChangeType.NothingChanged:
            case ChangeType.NotPresent:
                break;

        }

        return diffResult;
    }
}