/// <summary>
/// Restores the subject to the previous state on the undo stack, and stores the state before undoing to redo stack.
/// Method <see cref="CanUndo()"/> can be called before calling this method.
/// </summary>
/// <seealso cref="Redo()"/>
public void Undo()
{
if (tempMemento != null)
{
throw new InvalidOperationException("The complex memento wasn't commited.");
}
inUndoRedo = true;
IMemento <T> top = undoStack.Pop();
redoStack.Push(top.Restore(ref subject));
inUndoRedo = false;
}
/// <summary>
/// Internal <b>DO</b> action with no error checking
/// </summary>
/// <param name="m"></param>
private void _Do(IMemento <T> m)
{
redoStack.Clear();
undoStack.Push(m);
}