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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: ADA Popularity Discussion Request
Date: Sat, 11 Sep 2004 11:44:56 +0000 (UTC)
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Date: 2004-09-11T11:44:56+00:00
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Kevin Cline <kevin.cline@gmail.com> wrote:
 
: I don't know.  It could be done in C++ if Some_Index_Type had the
: right properties.  But as a practical matter, no one seems to care, at
: least no one in the C++ community.

Could it be an effect of tradition? If C++ had not inherited C arrays,
maybe arrays (including dynamically sized) were used more frequently?
I guess vector is used for array computation, then?

:  I very rarely have any need or use
: for a statically sized array.

If you need _dynamically_ sized arrays you still can have subtypes with
bounds determined at run time. I think this can be important. (C99 now
has some of it.) Declare the subtypes locally as index types, ranges
based on runtime values. Declare dynamically or statically sized arrays
in blocks, in functions, wherever.  Create corresponding arrays on the
stack or on the heap, assign the results ...


   type Vec is array (Positive range <>) of Natural;
   --   base type of all "vectors" counting from 1

   function make(limit: Positive; init: Natural := 0) return Vec
	--   a dynamically sized `Vec`, all values set to `init`
   is
      subtype Index is Positive range Positive'first .. limit;
      subtype A is Vec(Index);
   begin
      return A'(others => init);
   end make;

   x: Vec := make(5);

   pragma assert(x'first = 1 and x'last = 5);


-- Georg