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From: "Nasser M. Abbasi" <nma@12000.org>
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 17:29:46 -0700
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Date: 2010-10-15T17:29:46-07:00
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On 10/15/2010 5:16 PM, Adam Beneschan wrote:
> On Oct 15, 4:31 pm, "Vinzent Hoefler"<nntp-2010...@t-


>
> It seems like it would be simple to add syntax to array aggregates in
> the language like
>
> a : array(1..N) of Float := (for I in 1..N =>  Float(I)*Float(I));
>
> The legality rules and rules about applicable index constraints would
> be the same as if "for I in" were not present.
>
> Perhaps someone has already made a similar proposal, but I can't find
> it.  Since Ada 2012 is already putting "if" and "case" in expressions,
> though, it shouldn't be too big a leap to include "for" in an
> expression.  Of course, it's too late to make it into Ada 2012, but
> perhaps I'll propose it for the next version of Ada (what is that
> going to be?  Ada 2020, where we add all the features that we realize
> in hindsight that we should have added earlier? :-)).
>
>                                         -- Adam
>

That would be neat if this can be done. Because many times one needs to 
init an array or a matrix to some initial values, it is a bit more 
concise if one can do it in the 'same place' but Mr Robert Duff send me 
a nice solution to use, which is to use an init() function. Here is my 
code now using his idea. So, using his solution, it is almost as good as 
doing the initialization 'in place'.


-----------------------------------
-- gnatmake main.adb
-- platform: gcc 4.5 with Ada support.
--
with ada.float_text_io; use ada.float_text_io;
with ada.text_io; use ada.text_io;

procedure main is
      initial_h : constant float   := 1.0/8.0;
      nIter     : constant integer := 6;
      type h_type is array(1..nIter) of float;

      -- INIT function to use to initialize array h below
      function Init_h return h_type is -- NEED THIS HERE
      begin
          return result : h_type do
              for i in Result'Range loop
                  Result(i) := 1.0/(2.0**i);
              end loop;
          end return;
      end Init_h;

      h : constant h_type := init_h; -- INIT the array here

begin
     for i in  h'range loop
         put(h(i));
         new_line;
     end loop;
end main;
-------------------------------------

$ gnatmake main.adb
$ ./main.exe
  5.00000E-01
  2.50000E-01
  1.25000E-01
  6.25000E-02
  3.12500E-02
  1.56250E-02


--Nasser