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Subject: controlled types and point of instanciation
From: Mehdi Saada <00120260a@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:51028
Date: 2018-03-16T07:39:10-07:00
List-Id: <comp.lang.ada>

I make the humble request of an exegesis of this text: (from ada 95 the cra=
ft of oriented programming)
"Since Ada.Finalization.Limited_Controlled and Ada.Finalization.Controlled =
are both library-level types, all controlled types must be derived by insta=
ntiation at library level. Since generic packages are treated as being decl=
ared at the point of instantiation, this means that JE.Lists can only be in=
stantiated at library level, usually within the specification of another li=
brary package. This means that we can no longer use JE.Lists to build opaqu=
e types as [bellow]. Instantiating JE.Lists inside a package body is no lon=
ger permissible."

--> it refers to that:
package JE.Stacks is
-- anything
private
   type Stack_Item;
   type Stack_Type is access Stack_Item;
end JE.Stacks;

with JE.Lists;
package body JE.Stacks is
   package Lists is new JE.Lists (Item_Type);
   type Stack_Item is
   record
      L : Lists.List_Type;
   end record;
... end JE.STACKS;

So that I can grasp the rule better, what are the anomalous cases this rule=
 wants to avoid ?