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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: 'for cursor in container.first loop' bug?
Date: Thu, 28 Aug 2014 21:46:32 +0100
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Date: 2014-08-28T21:46:32+01:00
List-Id: <comp.lang.ada>

While scratching my head over 5.5.2 Generalized Loop Iteration, I looked
at A.18.32 Example of Container Use[1] and tried compiling with GNAT GPL
2014 and GCC 4.9.0. The full example compiled fine, but when I attempted
the substitution in (29) this happened:

    55.          -- Update minimum distance to newly reachable nodes.
    56.          for E of G (Next) loop
    57.             if not Reached(E.To) then
    58.                Nearest_Distance := E.Length + So_Far(Next);
    59.                if Nearest_Distance < So_Far(E.To) then
    60.                   Reached_From(E.To) := Next;
    61.                   So_Far(E.To) := Nearest_Distance;
    62.                end if;
    63.             end if;
    64.          end loop;

(so the original was OK, but ...)

    65.          for C in G (Next).Iterate loop
    66.             declare
    67.                E : Edge renames G (Next)(C).all;
                                        |
        >>> access type required in prefix of explicit dereference

    68.             begin
    69.                if not Reached(E.To) then
                                      |
        >>> invalid prefix in selected component "E"

    70.                   Nearest_Distance := E.Length + So_Far(Next);
                                              |
        >>> invalid prefix in selected component "E"

    71.                   if Nearest_Distance < So_Far(E.To) then
                                                       |
        >>> invalid prefix in selected component "E"

    72.                      Reached_From(E.To) := Next;
                                          |
        >>> invalid prefix in selected component "E"

    73.                      So_Far(E.To) := Nearest_Distance;
                                    |
        >>> invalid prefix in selected component "E"

    74.                   end if;
    75.                end if;
    76.             end;
    77.          end loop;
 

[1] http://www.ada-auth.org/standards/12rm/html/RM-A-18-32.html