Re: A suggestion for resource management

[stefan-lucks@see-the.signature]

On Sat, 21 Aug 2010, Florian Weimer wrote:

> The example at the end of section B.4 could use the Scoped pragma in
> this way:
> 
>           procedure Test_External_Formats is
>              ...
>              COBOL_File : File_Type;
>              ...
> 
>           begin
>              Open (COBOL_File, Name => "Some_File");
>              pragma Scoped (Close (COBOL_File));
> 
>              loop
>                ...
>           exception
>              when End_Error => ...
>           end Test_External_Formats;
> 

I don't quite why this needs an extra pragma -- your example is, 
apparently, easy to handle by current Ada's capacities:

          procedure New_Test_External_Formats is
             ...
             COBOL_File : File_Type;

             procedure Close_Cobol_File is
             begin
                Close(COBOL_FILE);
             end Close_Cobol_File;

             Finisher: Finish_Package.Finisher;
               -- The type Finish_Package.Finisher is derived from 
               -- Ada.Finalization.Limited_Controlled. 
             ...

          begin
             Open (COBOL_File, Name => "Some_File");
             -- pragma Scoped (Close (COBOL_File));
               -- we don't need the pragma
             Finisher.Set(Close_Cobol_File'Access);
               -- we will call Close_Cobol_File 
               -- when Finisher goes out of scope
             loop
               ...
          exception
             when End_Error => ...
          end Test_External_Formats;

The only disadvantage of this approach, in comparison to your pragma, is 
the need to define a parameterless procedure Close_Cobol_File. But 
defining such parameterless procedures is a design pattern you get used to 
anyway, when working with Ada.Containers. 





-- 
------ Stefan Lucks   --  Bauhaus-University Weimar  --   Germany  ------
               Stefan dot Lucks at uni minus weimar dot de
------  I  love  the  taste  of  Cryptanalysis  in  the  morning!  ------