Re: Instantiating package problems

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

Ok, so basically, my way of thinking about OOP in Ada is flawed.  All packages, by default, are static (as well as their methods), but if I want to call a method (procedure/function) I would have to do this on a type that's inside of a package, yes?

On Sunday, January 3, 2016 at 3:27:29 PM UTC-5, Georg Bauhaus wrote:
> On 03.01.16 19:40, Andrew Shvets wrote:
> > Hi all,
> >
> > 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.
> 
> The C++ equivalent of a generic package of Ada would be
> 
> (a) a generic namespace (with an optional block of statements
> that are executed when the namespace is elaborated), or
> 
> (b) a generic file that has, alongside any definitions, also said block
> of statements.
> 
> C++ is different from Ada in this regard, since it has generic types
> only and none of the above, except for preprocessor tricks.
> Ada, OTOH, does not have generic types, only generic units (possibly
> containing types) such as packages and subprograms.
> 
> "Calculator" of your example names a package, but not a (sub)type,
> this is what the compiler says in its first message.
> 
> If it is a generic package, then you'd be instantiating packages
> from it, but not objects. Again, unlike C++, which provides for
> some automatically inferred instantiations, Ada requires that
> generic units be instantiated explicitly.
> 
> > OUTPUT:$ gnatmake -g main.adb calculator.adb
> > gcc -c -g main.adb
> > main.adb:10:10: subtype mark required in this context
> > main.adb:10:10: found "calculator" declared at calculator.ads:5
> > main.adb:22:60: invalid prefix in selected component "Calc"
> > gnatmake: "main.adb" compilation error
> > =========================================================
> >