Re: Ada.Containers and concurrent modification exception.

[rakusu_klein@fastmail.jp]

среда, 19 сентября 2018 г., 18:53:31 UTC+3 пользователь Simon Wright написал:
> 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 — a bug or a feature.

Honestly, I just try to implement a standard containers in Ada by myself for educational purposes. In process I looking in GNU Classpath sources for an advice, and notice, that they are used an int counters (an int in Java have wrap-around semantic) in both containers and iterators for preventing working with invalid iterators. They call this a “fail-fast semantic”. So I decided to implement my own containers in that way, for example:
private
   type State_Type is mod 2 ** Integer'Size;

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

   type Map_Access is access constant Map;

   type Cursor is
      record
         Container : Map_Access  := null;
         State     : State_Type  := State_Type'First;
         Node      : Node_Access := 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, — it makes invalid any other Cursors. It may be stupid, 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.