Re: Ada.Numerics.Long_Real_Arrays

[Simon Wright <simon@pushface.org>]

hnptz@yahoo.de writes:

> with Ada.Numerics.Long_Real_Arrays; use Ada.Numerics.Long_Real_Arrays;
> package nm is
>
> Np : Positive;

So what value does Np have at this point?

> Type R_Vector is new Real_Vector (1..Np);

Np here will have whatever value it has been assigned by the compiler;
on my system, it was 0 (which isn't valid for Positive, but I expect the
compiler is allowed to make an undefined value whatver is convenient for
it).

> Type R_Matrix is array (Positive range <>) of R_Vector;
>
> procedure nm1 (P : in out R_Matrix);
>
> end nm;

> now in procedure test_nm.adb (only definitions):
>
> Np : Positive := 2;

This is a local declaration which hides Nm.Np (even if you "use Nm;");
setting a value here has no effect on Nm.Np.

> Mp : Positive := Np+1;
>
> 24  P : R_Matrix(1..Mp) := ((x,x),(y,y),(z,z));
>
> no "build all" error or warning

Because it's quite legal to have an array with index range 1 .. 0 -- it
just means it's empty (zero length).

> result when running:
>
> raised CONSTRAINT_ERROR : test_nm.adb: 24 length check failed.

Why not use Ada.Numerics.Long_Real_Arrays.Real_Matrix?