Re: Ada.Containers and concurrent modification exception.

[Jacob Sparre Andersen <jacob@jacob-sparre.dk>]

rakusu_klein@fastmail.jp writes:

> Why Ada's Cursors does not provide the
> ConcurrentModificationException, as Java Collections do,

Because that is something from Java. ;-)

> or some variant of it?

The Ada containers define the concept of tampering.  I can't remember
which exception you get in case you tamper with a standard container,
but you can be pretty sure you will get one.

> Consider the following:
>
> with Ada.Containers.Indefinite_Ordered_Maps;
> ...
>    The_Map : Map;
> ...
> declare
>    I : Cursor := First (The_Map);
>    J : Cursor := First (The_Map);
> begin
>    --  Now Cursors are synchronized with each other and with a container.
>    Delete (The_Map, I);
>    --  It's O'k. But now J lost a sync and points to a dead Node.
>    Next (J);
>    --  What should I expected here,
>    --  any well defined exception or
>    --  raising a zombie?
> end;

Did you try it?

Both with GCC 6.3.0 and with GNAT CE 2018 I get
System.Assertions.Assert_Failure, but that is definitely not defined as
a part of the tampering checks, so I suspect GNAT is wrong (but still
safe) here.

I've posted an executable example here:

https://bitbucket.org/sparre/ada-2012-examples/src/default/src/container_tampering.adb

(Randy, feel free to adapt it for ACATS, if it shows something relevant)

Greetings,

Jacob
-- 
"In case of discrepancy, you must ignore what they ask for
 and give what they need, ignore what they would like and
 tell them what they don't want to hear but need to know."
                                                 -- E.W. Dijkstra