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Subject: Re: Safety of unprotected concurrent operations on constant objects
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Date: 2014-05-04T14:25:26-06:00
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On 04-May-14 01:46, Natasha Kerensikova wrote:
> I have some shared resources indexed by a string, described in a
> file, and considered as constant throughout the lifetime of the program
> (with the standard scheme "restart for changes to take effect").

What's the problem, then, with making the entire map constant?

  Some_Map : Constant Ordered_Map:= Load_From_File;

Or, I suppose, something like wrapping it in a protected object?
(Then you have its accesses blocked off.)

----------

As a matter of last resort you could use a package:

Package Data_Map is

   Function Get( Index: String ) return Data_Type;

   No_Index : Exception;

End Data_Map;

Package Body Data_Map is

   Type Item_List is Array(Positive Range <>) of Unbounded_String;

   Function Load_From_File return Item_List is
   -- ...

   Implementation : constant Item_List:= Load_From_File;

   -- Naive linear-search; could be optimized, provided Load_From_File
   -- returns its list as a sorted list... for small data-sets this
   -- should suffice.
   Function Index_Of( Item : String ) Return Positive is
   begin
     For Index in Implementation'Range loop
      if Implementation(Index) = To_Unbounded_String(Item) then
        Return Index;
      end if;
     end loop;

     Raise No_Index;
   end Index_Of;

   Function Get( Index: String ) return Data_Type is
     Item_Number : Positive renames Index_Of(Index);
   begin
     Return Result : constant Data_Type := Implementation( Item_Number );
   end Get;

End Data_Map;