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From: "Adam Beneschan" <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Loop parameter type
Date: 25 Sep 2006 17:12:33 -0700
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Date: 2006-09-25T17:12:33-07:00
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Maxim Reznik wrote:
> Hi, All
>
> Please help me understand Ada name resolution rules for
> loop parameter specification.
>
> Consider follow code:
>
>  1: procedure Test is
>  2:    type Int is range 0 .. 1000;
>  3:    C     : Integer := 0;
>  4:    C_Int : Int := 0;
>  5: begin
>  6:    for J in 1 .. 10 loop
>  7:       C := C + J;
>  8:    end loop;
>  9:
> 10:    for K in 1 .. 10 loop
> 11:       C_Int := C_Int + K;
> 12:    end loop;
> 13: end Test;
>
> gcc -c test.adb
> test.adb:11:22: invalid operand types for operator "+"
> test.adb:11:22: left operand has type "Int" defined at line 2
> test.adb:11:22: right operand has subtype of "Standard.Integer" defined
> at line 10
>
> GNAT complains at line 11, but line 7 seems Ok. Why?
>
> I expect range 1 .. 10 is root_integer type, because of preference
> root_integer over others integer types.
> ARM states: "There is a preference for the primitive operators (and
> ranges) of the root numeric types root_integer and root_real."

Bob and Jeff have already explained why the types of J and K are of
type Standard.Integer and not root_integer.  You should also be aware
that if J and K *were* root_integer, then you'd get two errors instead
of one, because there is no predefined + operation whose left operand
is Standard.Integer or Int, and whose right operand is root_integer.
You're probably confusing this with universal integers.  A universal
integer can appear any place that *any* integer type is expected.  But
a value of type root_integer is *not* a universal integer and doesn't
have that property.

                          -- Adam