Re: Ada.Containers and concurrent modification exception.

["Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>]

On 09/19/2018 03:12 PM, rakusu_klein@fastmail.jp wrote:
> 
> 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;

The ARM covers this case in ARM A.18.4(76-80) [I am unable to access the current 
ARM right now, so I'm quoting from ISO/IEC 8652:2007, which should be similar]:

"A Cursor value is invalid if ... The node it designates has been deleted from 
the map. The result of "=" or Has_Element is unspecified if these functions are 
called with an invalid cursor parameter. Execution is erroneous if any other 
subprogram declared in Containers.Hashed_Maps or Containers.Ordered_Maps is 
called with an invalid cursor parameter.

So J is invalid and Next (J) is erroneous. ARM 1.1.5(10) defines erroneous 
execution: "there is no language-specified bound on the possible effect of 
erroneous execution; the effect is in general not predictable." In other words, 
this call can do anything.

-- 
Jeff Carter
"I spun around, and there I was, face to face with a
six-year-old kid. Well, I just threw my guns down and
walked away. Little bastard shot me in the ass."
Blazing Saddles
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