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From: Bob Duff <bobduff@theworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Instantiating package problems
Date: Sun, 03 Jan 2016 17:08:37 -0500
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Date: 2016-01-03T17:08:37-05:00
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Andrew Shvets <andrew.shvets@gmail.com> writes:

> This is coming from the perspective of someone that has far more C++ OOP
> experience.

Ada has "packages" and "types".  C++ combines these into one feature
(the "class").  I suspect that difference explains your confusion.

>...Basically, what I'm trying to do is create an instance of a
> package and then call a function from that object.

There's no such thing as an instance of a package in Ada.
An instance of a generic package (which is sort of like a C++ template)
is a package, not an object.  An instance of a type is
an object.

>...This is what I have below.
> The calculator package is a simple package with the Addition function (which,
> you guessed it, just adds numbers together) that takes two integers and returns
> an integer.
>
> I think I'm not quite getting this right or I've misunderstood something.  Here
> is my code so far and the results that I get when I compile it.
>
> =========================================================
> with Ada.Text_IO;
>
> with Calculator;
>
> procedure Main is
>   Calc : Calculator;

Better to show a complete example.

But anyway, Calculator is a package, not a type.
I think you can get rid of this line.
I'm guessing there are no types declared in Calculator.

> begin
>   ...
>
>   Ada.Text_IO.Put_Line(" Addition:       " & Integer'Image(Calc.Addition(52, 31)));

I think you can just call Calculator.Addition.  I can't be sure without
a complete example.

By the way, I don't see anything object-oriented in this example.
It looks like you're just trying to call a function that is declared
in a package -- no need to create any objects here.

>   Ada.Text_IO.New_Line;
> end Main;
>
> OUTPUT:$ gnatmake -g main.adb calculator.adb

You don't need to tell gnatmake all the files.  Just the main
procedure -- it can find all the other files that need to be
[re]compiled based on the "with"s (etc.).

- Bob