Lack of `outer` keyword makes inner class dup implossible

[Derek Parnell]

On Sat, 15 Jul 2006 17:50:11 +1000, S. <dnewsgr at mephit.kicks-ass.org>  
wrote:

> On 2006-07-14 21:10:41 -0700, "Derek Parnell" <derek at psych.ward> said:
>
>> Ok, assuming that 'nested' and 'inner' are synonymous in this  
>> discussion,  it appears that their main purpose is to provide scope  
>> limitation. That  is, the functionality provided by inner  
>> classes/functions is restricted  to, and there by only relevant to, the  
>> containing class/function.
>>  I use inner functions this way because I can see their utility, but  
>> can  someone supply a good inner class example? As far as I can see,  
>> an  instance of an inner class only makes sense in the context of its  
>> parent  class and is thus reliant on the 'outer' class for relevancy.  
>> I'm having  trouble visualizing where this might be a Cool Thing(TM).
>
> I'm writing a Sudoku solver.  I have a Cell class, an individual cell is  
> only relevant in the context of the board.  It makes various things a  
> Cell might want to do easier having access to information about the  
> board it lives on.  I could pass it a board instance when I create it  
> like I did originally, but I saw nested classes and thought it was a  
> nifty feature.

So the main reason is so Cell objects can access the Board object's  
members.

This can also be done just by declaring the classes in the same module,  
and thus avoid the restrictions you are tripping up on.

==============
module board;

class Board
{
    private Cell[9][9] arena;
    private int option_x;
    private bool Solved()
    {
      . . .
    }
    . . .
}

class Cell
{
    private Board owner;

    this(Board b)
    {
       if (b.option_x)
       {
         . . .
       }
       owner = b;
    }

    this(Cell c)
    {
       owner = c.owner;
    }
    Cell dup()
    {
       return  new Cell(this);
    }

    bool Set()
    {
      . . .
      return owner.Solved();
    }
}

================

Its just an alternative using current D syntax. No big deal ;-)

-- 
Derek Parnell
Melbourne, Australia