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Date: Fri, 07 Mar 2008 11:51:49 +0100
From: Georg Bauhaus <rm.tsoh.plus-bug.bauhaus@maps.futureapps.de>
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Subject: Re: default formal parameters in generic declarations
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Date: 2008-03-07T11:51:50+01:00
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Ludovic Brenta wrote:
> Eric Hughes writes:
>> On Mar 6, 2:32 am, Georg Bauhaus wrote:
>>> By way of speculation, can nesting, to the extent it is absent from C++,
>>> lead to at least a partial solution of this problem?
>> [example deleted]
>>  I note here that your example uses a formal
>> default subprogram.

> The actual subprogram may very well be nested in a package that
> declares all the necessary types and variables to keep the state.

Yes, and in C, too, a local static struct might keep state.
But actually, the function in the example,

generic
   Additional_Operations_Object: Functionality_Interface'Class :=
      Add_Ops_Factory.New_Object;
package Foo is

   type T is ...

is used only to provide a default object of a suitable abstract
type (which could be Any'Class) on instantiation. This object
can be overridden, passed downwards to other instantiations,
"intercepted" by different Functionality_Interface'Class objects...
But, as Eric has explained, going along this path does not
yet lead to complete solution.