Re: Unconstrained Arrays

[belteshazzar <gbelteshazzar@gmail.com>]

On Mar 17, 11:49 am, "Jeffrey R. Carter"
<spam.jrcarter....@spam.acm.org> wrote:
> belteshazzar wrote:
> > I have a program that uses a lot of different sized arrays and passed
> > into math functions. So I'm using an unconstrained array type. The
> > problem that I have is that I'm not allowed to use "new" this means
> > that I have to use pools (which I can't because to intantiate a pool I
> > have to constrain the array type) or allocated the arrays on the
> > stack. Allocating the arrays on the stack is fine, BUT it means that i
> > have to use array initializers so that they remain unconstrained
> > rather than becoming an anonomous contrained type that can no longer
> > be passed to my math functions.
>
> I'm not clear what you're talking about. You can pass a constrained subtype to a
> subprogram that takes a parameter of an unconstrained array type.
>
> For example, String is an unconstrained array type. If we have
>
> function F (S : in String) return Natural;
>
> V : String (1 .. 10);
> C : Natural;
>
> then it's perfectly legal to call F with V as its actual parameter:
>
> C := F (S);
>
> > Also, and the main point of my post, I've found that I can place the
> > unconstrained array inside a record with a distriminant and this seems
> > to solve all our problems. We don't have to use array initialisers and
> > we can get pointers to aliased objects that can be easily passed to
> > the math functions.
>
> Here is your problem. There should be no reason to pass explicit pointers to
> these functions. Your best solution is to rewrite or change your library.
>
> --
> Jeff Carter
> "Drown in a vat of whiskey. Death, where is thy sting?"
> Never Give a Sucker an Even Break
> 106

As we have very large array's we're using something like:


type Unconstrained_Array is array ( Integer range <> ) of Integer;
type Unconstrained_Array_Pointer is access all Unconstrained_Array;

procedure F (S : in Unconstrained_Array_Pointer);

V : Unconstrained_Array := (1 .. 10_000 => 0);
V_Ptr : Unconstrained_Array_Ptr :=
Unconstrained_Array'unchecked_Access

F (V_Ptr);


Note the use of the array intialiaser, if this isn't used then the
pointer is no longer compatible.