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From: "jimmaureenrogers@worldnet.att.net" <jimmaureenrogers@worldnet.att.net>
Newsgroups: comp.lang.ada,comp.lang.fortran,comp.lang.pl1
Subject: Re: Bounds Check Overhead
Date: 27 May 2006 08:53:44 -0700
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Date: 2006-05-27T08:53:44-07:00
List-Id: <comp.lang.ada>

Ludovic Brenta wrote:
> "robin" writes:
> > "Simon Wright" writes:
> >> In Ada one should where possible use the 'Range attribute:
> >
> > Ideally yes, but in practice, such as in sorting and averaging,
> > the loop is often one or two short of the number of elements in the array.
>
> No problem:
>
> type Some_Array_Type is array (Positive range <>) of Something;
>
> procedure Walk (A : in Some_Array_Type) is
> begin
>    for J in A'First .. A'Last - 1 loop
>       ...
>    end loop;
> end Walk;

A somewhat more general syntax is also available.
Ada allows indexing of arrays using any discrete type.
Discrete types include integer types and enumeration types.
Enumeration types have no arithmetic operators.

generic
   type Element_type is private;
   type Index_Type is (<>);
   type Some_Array_Type is array (Index_Type range <>) of Element;

procedure Wal(A : in Some_Array_Type) is
begin
   for J in A'First .. Some_Array_Type'Pred(A'Last) loop
      ...
   end loop;
end Walk;

The 'Pred attribute evaluates to the value preceding the value
specified by its actual parameter. The effect is to iterate from the
first index value to one before the last index value.

Jim Rogers