Re: Dynamic array allocation and STL equivalents?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 11 Feb 2005 05:06:56 -0800, brian.b.mcguinness@lmco.com wrote:

[...]

Dynamic allocation of arrays is no problem in Ada.

> One interesting project would be to create an object class hierarchy to
> implement APL arrays.  In APL, the lengths of an array's dimensions can
> change, e.g. by concatenating new rows or columns onto a matrix, or
> concatenating two matrices, and the number of dimensions can also
> change, e.g. by "laminating" two 12x30 arrays to form a 2x12x30 array.
> In C++, an obvious solution would be to use STL vectors, e.g.:
> 
> class RealArray {
>   private:
>     vector <unsigned long> dimensions;
>     vector <double>        data;
>   public:
>     // define an indexing operator[] to use the dimensions
>     // vector to translate sets of indices into offsets
>     // into the data array

Index of a multi-dimensional array is a tuple. That won't work in C++ (you
cannot override "," to support: A[i,j,k]). Neither works it in Ada.

Though in Ada you could have a type:

   type Index is array (Integer range <>) of Integer; -- Tuple

then in Real_Array:

   type Real_Array is private;
   function Get (Container : Real_Array; Element : Index) return Float;

private
   type Index_Ptr is access Index;
   type Real_Array is new Ada.Finalization.Controlled with record
      Lower_Bound : Index_Ptr;
      Upper_Bound : Index_Ptr;
      Data : <whatsoever>
   ...
   procedure Finalize (X : in out Real_Array);
      -- Destructor is a handy thing

Then you could index your arrays like:

Get (My_Array, (I, J, K));

Further, if you wished to support slices sub-matrices etc, that would
require a lot of work. Alas, in Ada you cannot override either "()" or ".."
or "in" (membership test) or aggregates. So the interface would be rather
clumsy.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de