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From: "G.B." <bauhaus@notmyhomepage.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Bad cursor, good cursor
Date: Mon, 27 Mar 2017 20:12:07 +0200
Organization: A noiseless patient Spider
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Date: 2017-03-27T20:12:07+02:00
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On 27/03/2017 18:56, Marius Amado-Alves wrote:
> Ada 2012 compiled with latest(?) free GNAT (20160515-19)
>
> This breaks with a "bad cursor" error for Subthing_Maps.Element at line 7. But how can that be, if the cursor has just been vetted at line 6 as not No_Element, and there were no changes to the container meanwhile, not even navigation?
>
> 1   C := Thing.Find (Thing_ID);
> 2   if C = Thing_Maps.No_Element then
> 3      Thing.Insert (Thing_ID, Subthing_Maps.Empty_Map, C, Ok);
> 4   end if;
> 5   I := Subthing_Maps.Find (Thing_Maps.Element (C), Subthing_ID);
> 6   if I = Subthing_Maps.No_Element
> 7   or else Subthing_Maps.Element (I) = Preterred then
> 8      Thing.Update_Element (C, Add_Subthing'Access);
> 9   end if;

Are Thing_Maps and Thing different?  Thing.Insert involves C,
which is then passed to Thing_Maps.Element.
Just an observation, even though it isn't obviously connected
with  I.

Is there overlap in some form or other, of things involved?