// Modifying methods.
public void AddUnit(UnitCore unit, Vector2Int position)
{
if (unit is null)
{
throw new ArgumentNullException(nameof(unit));
}
var onPosition = this[position];
if (onPosition != null)
{
throw new InvalidOperationException($"Position {position} is already occupied by {onPosition}.");
}
unit = unit.Clone();
unit.Connect(Presentation);
presentationsToUnits[unit.Presentation] = unit;
unitsToPositions[unit] = position;
positionsToUnits[position] = unit;
state = state.BuildTransition(unit.Presentation);
}
