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From: Gene <gene.ressler@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: initialize an array (1-D) at elaboration using an expression
 based on the index?
Date: Fri, 15 Oct 2010 17:54:05 -0700 (PDT)
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Date: 2010-10-15T17:54:05-07:00
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On Oct 15, 7:03=A0pm, "Nasser M. Abbasi" <n...@12000.org> wrote:
> Ada experts:
>
> I am not able to find an example on this.
>
> I was wondering if in Ada I can initialize some array, where I can fill
> the content of each entry in the array based on some function of the inde=
x?
>
> For example, in Fortran one can do this:
> -----------------------
> program main
> =A0 =A0integer, parameter :: N =3D 10
> =A0 =A0real, dimension(N) :: a=3D(/(j**2,j=3D1,N)/)
>
> =A0 =A0print*, a
> end program
> ------------------------
> $ gfortran t3.f90
> $ ./a.exe
> =A0 =A0 1.0000000 =A0 =A0 =A0 4.0000000 =A0 =A0 =A0 9.0000000 =A0 =A0 =A0=
 16.000000 etc....
>
> In Ada, what would I need to do in the initialization below?
> ---------------------------
> procedure t2 is
> =A0 =A0 N: constant integer :=3D 10;
> =A0 =A0 a: array(1..N) of float :=3D (others=3D>0.0); --??
> begin
> =A0 =A0 null;
> end t2;
> -----------------------------
>
> I know ofcourse I can initialize it in the body by a loop, just wanted
> to see if it is possible to do it in the elaboration.

It's ugly, but you can get the effect with something like:

  Initializer_Index : Natural :=3D 0;

  function Initial_Function_Of_Index return Float is
  begin
    Initializer_Index :=3D Initializer_Index + 1;
    return 2.0 * Float(Initializer_Index);
  end;

  A : array(1 .. 100) of Float :=3D (others =3D>
Initializer_Function_Of_Index);

What you're asking about is called a comprehension or list
comprehension. I agree it would be nice to have them.