Hiding methods that shouldn't be call-able.

[chronozphere]

Hey guys,

I have a question for you.

Lets say you've made program containing to modules A and B. There is an object of type X that is known in both modules. X has 4 methods:

> P and Q that should only be called from the code inside module A.
> R and S that should only be called from the code inside module B.

How would you fix this? Just make all methods public and write proper documentation on how to use them, or make a strict separation by using interfaces or something else?

I feel that creating a strict separation makes my program overly complex, while just making everything public feels dirty.

Any ideas?

Thanks

[JSoftware]

I think the sane thing to do would be to make both public. Always try to make your code as secure as possible, but making sure some procedures only can be called in certain units would be bad design

Can't you place the superclass in module A and derive another class in module B? That was P and Q can be protected, and R+S can be protected in module B?

[chronozphere]

The downside of your inheritance approach is that both private/protected methods can only be used in one unit. Depending on how our X object is used, this can mean that the entire module A must be defined in one unit. I really prefer to split large modules in multiple units, each having 1-5 classes. I not too keen on this "unit scope" thing that pascal has.

Personally, I think other languages do a better job at this. C++ has "friend classes" (though they can be messy). Java has packages. These give you a lot more accessibility control for your classes.

[User137]

Isn't C++'s "#include" almost equivalent to Pascal call "uses"? But that talk goes about namespaces...

You have another option, module C from wich module A and B are used and controlled together.

[virtual]

C++ has "friend classes" (though they can be messy). Java has packages

The equivalent in Delphi is to declare package or friend classes in the same unit, which gives them access to the private and protected parts of every class defined in the same unit.

from : Delphi in a Nutshell

[Mirage]

The both answers in the poll are wrong. First is impossible, second is too bad.
You obviously can't hide parts of public interface depending on interface requester regardless of programming language. How you can do it with C++ or Java?
But you can easily have several interfaces of object X suitable for each module.
Example implementation:

unit xxx; // ;)
interface
type
  IXForA = interface
    procedure P();
    procedure Q();
  end;

  IXForB = interface
    procedure R();
    procedure S();
  end;

function GetXForA(): IXForA;
function GetXForB(): IXForB;

implementation

type
  TX = class(IXForA, IXForB)
  ...
    procedure P();
    procedure Q();
    procedure R();
    procedure S();
  end;

function GetXForA(): IXForA;
begin
  Result := TX.Create();
end;

function GetXForB(): IXForB;
begin
  Result := TX.Create();
end;

This way it will hard to use both interfaces at the same time.

Also you can make private (or protected) all the 4 methods and place the functions GetXForA()/GetXForB() as public ones into class X.

Aggregated classes can be used instead of interfaces for better performance.

Aggregating classes is another approach.