Re: how to import a package

["Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>]

markww wrote:
> Yes I'm still confused - sorry - I'm coming from C++ / java and the ada
> syntax / scoping is a bit strange to me. So I thought a package is
> equivalent to a structure/class.

A package provides modularity, encapsulation, information hiding, and 
namespace control. A C++ struct is the equivalent of an Ada record type. 
A C++ class provides encapsulation and information hiding. C++ 
namespaces provide namespace control. Nothing in C++ provides 
modularity, although header files and preprocessor textual inclusion 
provide an imitation.

> I thought that the following line:
> 
>     package Person_List in new P (T => PERSON_REC)
> 
> is just instantiating one instance of the package called Person_List.

Right. P is a generic package, and this creates an instantiation of it, 
a package named Person_List.

> So the line:
> 
>     Start : Person_List.Node_Ptr;
> 
> doesn't make sense to me since it looks like 'Start' is being defined
> as pointing to Person_List.Node_Ptr, when I thought the right side of
> the colon must be a data type.

Start is a variable object, of type Person_List.Node_Ptr. The type's 
simple name is Node_Ptr, but that's not visible. The expanded name 
(Person_List.Node_Ptr) means it's Node_Ptr in Person_List.

> In any event, I can't event get past adding the following line under
> the package:
> 
>      package Person_List is new P (T => PERSON_REC);
> 
> my compiler (gnat) gives an error saying:
> 
>     operator for type "Node_Ptr" defined at line 23, nstance at line 39
> is not directly visible
>     use clause would make operation legal

That's an odd msg; without more context I don't know what it's trying to 
tell you. This line has to come after the declaration of Person_Rec.

-- 
Jeff Carter
"People called Romanes, they go the house?"
Monty Python's Life of Brian
79