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Newsgroups: comp.lang.ada
Date: Wed, 19 Sep 2018 11:24:32 -0700 (PDT)
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Subject: Re: Ada.Containers and concurrent modification exception.
From: rakusu_klein@fastmail.jp
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Xref: reader02.eternal-september.org comp.lang.ada:54380
Date: 2018-09-19T11:24:32-07:00
List-Id: <comp.lang.ada>

=D1=81=D1=80=D0=B5=D0=B4=D0=B0, 19 =D1=81=D0=B5=D0=BD=D1=82=D1=8F=D0=B1=D1=
=80=D1=8F 2018 =D0=B3., 18:53:31 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=
=D0=B2=D0=B0=D1=82=D0=B5=D0=BB=D1=8C Simon Wright =D0=BD=D0=B0=D0=BF=D0=B8=
=D1=81=D0=B0=D0=BB:
> It would be a good thing if the error was detected. Perhaps submit a bug
> report to AdaCore?
I am new in Ada, so don't know what is it =E2=80=94 a bug or a feature.

Honestly, I just try to implement a standard containers in Ada by myself fo=
r educational purposes. In process I looking in GNU Classpath sources for a=
n advice, and notice, that they are used an int counters (an int in Java ha=
ve wrap-around semantic) in both containers and iterators for preventing wo=
rking with invalid iterators. They call this a =E2=80=9Cfail-fast semantic=
=E2=80=9D. So I decided to implement my own containers in that way, for exa=
mple:
private
   type State_Type is mod 2 ** Integer'Size;

   type Map is
      record
         State : State_Type  :=3D State_Type'First;
         Size  : Natural     :=3D Natural'First;
         Root  : Node_Access :=3D new Node_Object (Variant =3D> Empty);
      end record;

   type Map_Access is access constant Map;

   type Cursor is
      record
         Container : Map_Access  :=3D null;
         State     : State_Type  :=3D State_Type'First;
         Node      : Node_Access :=3D null;
      end record;

In operations with container I just compare States in Container and Cursor =
and throw a Concurent_Modification exception if they are not equal. If any =
operation   deletes a Node, I just increment States in Container and Cursor=
, if it used, =E2=80=94 it makes invalid any other Cursors. It may be stupi=
d, but works well for me.

After all I looked at the Ada.Containers and notice, that its Cursors does =
not have any kind of modification counters. So I decided to ask here about =
it.