Re: Instantiating package problems

[Andrew Shvets <andrew.shvets@gmail.com>]

On Sunday, January 3, 2016 at 4:04:16 PM UTC-5, Jeffrey R. Carter wrote:
> On 01/03/2016 11:40 AM, Andrew Shvets wrote:
> > 
> > This is coming from the perspective of someone that has far more C++ OOP
> > experience.  Basically, what I'm trying to do is create an instance of a
> > package and then call a function from that 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.
> 
> First you need to unlearn everything you've learned from using a poorly
> designed, error-prone language.
> 
> "Instantiate" in Ada is a technical term that refers to creating a package or
> subprogram from a generic. There don't appear to be any generics in your
> example, so your subject line is a bit misleading.
> 
> You haven't shown us Calculator, so we can't be sure what you're trying to do,
> but I'm going to guess that it looks like
> 
> package Calculator is
>    function Addition (Left : Integer; Right : Integer) return Integer;
> end Calculator;
> 
> If I'm wrong, then you can probably ignore everything else I'm going to say.
> 
> A pkg is a module. It provides encapsulation and information hiding. C++ doesn't
> have modules, which are an essential part of any language. A pkg is not a
> (sub)type, so you can't declare objects of it. A pkg just is. Once you say
> 
> with Calculator;
> 
> you have Calculator and you can refer to it, just like Ada.Text_IO. What you're
> probably trying to do is
> 
> with Ada.Text_IO;
> with Calculator;
> 
> procedure Test_Calculator is
>    -- The declarative part is empty, since no declarations are needed
> begin -- Test_Calculator
>    Ada.Text_IO.Put_Line
>       (Item => "Addition (52, 31): " &
>                Integer'Image (Calculator.Addition (52, 31) ) );
> end Test_Calculator;
> 
> -- 
> Jeff Carter
> "Who wears beige to a bank robbery?"
> Take the Money and Run
> 144

Ok, I see, I think.  I suppose a better analogy is how in C you use #include "Some_File.h" and all of the contents of that file just come in and can be used readily, yes?

I'm still a little bit lost on the below example:
https://en.wikibooks.org/wiki/Ada_Programming/Object_Orientation#Derived_types

Basically, an instance of a type inside of a package is created and that is used to work on.