3 dimension arrays

[Andrey via Digitalmars-d-learn]

On Thursday, 26 February 2015 at 23:25:22 UTC, Ali Çehreli wrote:
> On 02/26/2015 12:01 PM, Andrey wrote:> HI guys!!!
> >
> > Have a problem with 3d array memory allocation in next code:
> >
> > //////////////////////////////////////////////////////////
> > class NeuronNet(T, const uint layersNum)
> > {
> >      T[]                    _inputs;
> >      T[][layersNum - 2]    _hidden;
> >      T[]                    _outputs;
> >      T[]                    _target;
> >
> >      //waights [col][row][dimension]
> >      T[][][layersNum - 1] _waightsArray;
>
> (Unrelated: That may be a typo if its actually "weights".)
>
> >      this(in uint[] nodesArr)
> >      {
> >          //values init
> >          _inputs = new T[nodesArr[0]];
> >          _outputs = new T[nodesArr[$-1]];
> >
> >          for(uint j = 0; j < layersNum - 2; j++)
>
> Better:
>
>     foreach (j; 0 .. layersNum - 2)
>
> >          {
> >              _hidden[][j] = new T[nodesArr[j + 1]];
>
> You have extra [] up there. This is equivalent:
>
>              _hidden[j] = new T[nodesArr[j + 1]];
>
> The reason is, _hidden[] means "the entire _hidden slice" 
> anyway. So, the empty [] has no meaning at all.
>
> >          }
> >          //waights init
> >          for(uint i = 0; i < layersNum - 1; i++)
> >          {
> >              _waightsArray[][][i] = new T[][nodesArr[1+i]];
>
> Same there:
>
>              _waightsArray[i] = new T[][nodesArr[1+i]];
>
> >              for(uint ii = 0; ii < nodesArr[1+i]; ii++)
> >              {
> >                  _waightsArray[][ii][i] = new T[nodesArr[i]];
>
> You want to set ii'th element of the i'th element, right? This 
> is the right way to do it in D:
>
>     _waightsArray[i][ii] = ...
>
> Unlike C and C++, the array syntax is natural in D. In other 
> words, it is not "inside out".
>
>      T[] --> A slice of Ts
>      T[][] --> A slice of T slices
>      T[][][layersNum - 1] --> A number of those
>
> So, _waightsArray[i] is one of the slices that you've just set 
> in the previous for loop.
>
> Ali

I very much appreciate. The author of D-book respond to me. 
THANKS VERY MUCH!!!!!