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Subject: Tables vs functions (was Re: Anonymous array clarification.)
References: <tY1g7.45466$K6.17744072@news2> <3b80c13f$1@pull.gecm.com>
From: Ray Blaak <blaak@infomatch.com>
Message-ID: <un14uy8v0.fsf_-_@infomatch.com>
Organization: The Transcend
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Date: 20 Aug 2001 09:49:39 -0700
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Date: 2001-08-20T09:49:39-07:00
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"Phil Thornley" <phil.thornley@baesystems.com> writes:
> On the question of what they are used for, I most commonly use them for
> look-up tables.
> 
>    type Day is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
> 
>    Tomorrow : constant array (Day) of Day
>                      := (Tue, Wed, Thu, Fri, Sat, Sun, Mon);
> 
> (which avoids a lot of stuff about 'Succ and worrying about
> wrap-around).

Hmm.

function Tomorrow(A_Day : in Day) return Day is
  Result : Day;
begin
  if A_Day < A_Day'Last then
    Result := Day'Succ(A_Day);
  else
    Result := Day'First;
  end if;
  return Result;
end Tomorrow;

Doesn't seem too complicated, looks the same to the user, is just as time
efficient, is more space efficient, and works for any size of
array/enumeration type.

It also is more robust, since one does not have to tediously type out the
items in a possibly erroneous way.

On the other hand, tables are useful when the calculations are expensive,
difficult or tedious to describe algorithmically, or the values change
according to subsequent data inputs.

-- 
Cheers,                                        The Rhythm is around me,
                                               The Rhythm has control.
Ray Blaak                                      The Rhythm is inside me,
blaak@infomatch.com                            The Rhythm has my soul.