Renaming exceptions in private section?

Renaming exceptions in private section?

[Dale Stanbrough]

Looking through some data structure packages I noted
that many package specs required the use of an
instantiated generic, and would rename some of it's
exceptions.

e.g.

	with some_generic_package;

	package a is

		package b is new some_generic_package(some_type);
	
		overflow :exception renames b.overflow;
	
		....

In the case where no other resources from the generic are being
used by clients of package a, it would be better if the generic
were instantiated in the private section, and the exception
renamed there. However this doesn't seemed to be allowed.

When I tried...

	package fred is
	
		a: exception;
		
	private
		b: exception;
		a: exception renames b;
	end;
	
...Gnat complained that

	"a" conflicts with declaration at line 3
	
Is it possible to rename an exception in the private section
- sort of a deferred exception (similar to deferred constants)?

Dale

Re: Renaming exceptions in private section?

[Michel Gauthier]

In article <4l52fh$ivr@goanna.cs.rmit.edu.au>, Dale Stanbrough
<dale@goanna.cs.rmit.EDU.AU> wrote:

>>  [...]
>>  When I tried...
>>  
>>          package fred is
>>          
>>                  a: exception;
>>                  
>>          private
>>                  b: exception;
>>                  a: exception renames b;
>>          end;
>>          
>>  ....Gnat complained that
>>  
>>          "a" conflicts with declaration at line 3
>>          
>>  Is it possible to rename an exception in the private section
>>  - sort of a deferred exception (similar to deferred constants)?

Strictly speaking, no, but a good trick could be to use
Exception_Id~entities (see for instance my old paper 
in Ada Letters).

with Ada . Exceptions ;  
package fred is
       a: constant Ada . Exceptions . Exception_Id ;
       ...
private
        b: exception;
        a: constant Ada . Exceptions . Exception_Id := B ' Identity ;
end;

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