Re: Idiom for a class and an object in Ada

["Matthew Heaney" <mheaney@on2.com>]

"Marin David Condic" <nobody@noplace.com> wrote in message
news:M3Ocd.237$5i5.72@newsread2.news.atl.earthlink.net...
> Suppose I have a class with one or a limited set of objects. The objects
> are "global" in the sense that they hang around from program startup
> thru the entire life of execution. An example would be an A/D Converter
> class - My little control box might have 3 or 4 A/Ds in it - they're
> always there and I want the data associated with them to be static (not
> declared on the stack.)
>
> Question: What is the preferred Ada idiom for defining such a creature?

See for example the packages Data_Maps and Relation_Maps in the genealogy
examples in the ai302 examples subdirectory:

<http://charles.tigris.org/source/browse/charles/src/ai302/examples/genealog
y/>

The idea is to create a limited private type with an unknown discriminant:

package Data_Maps is
   type Map (<>) is limited private;
  ... -- operations here

   function Dates return Map;
   function Places return Map;
private
   ... -- see code for implementation
end;

This is similar to how Standard_Input, Standard_Output, etc are implemented
in Text_IO.