Berocoder

Hm ok. Thanks for the advice 🙂

9 hours ago, Uwe Raabe said:

What about TPerson -> TAbstractPerson -> TAmStateObject ?

Btw, that means I have to typecast every access  to the concrete class ?

The code I posted here is heavily simplified. I agree that cyclic dependencies is not good. 

But basically one class is one table in database for most cases. There is also some transient classes that reside only in memory.

So this is about relations between classes.

Many times I want to navigate both from class A to B and from B to A.

For example class TPerson have a relation to TAddress.
So to find the address:

  vAddress := aPerson.Address,AsString:;

But to find the person who live at an address make also sense

  vName := aAddress.Person.AsString;

So one way to break dependency is to use interface. But there are many questions left to work with as the whole framework now assume direct access.

So I want to work with IAddress and IPerson instead of TAddress and TPerson.

But at some point I must deal with the concrete class anyway.

About abstract classes, that is a good point. But what happens with the inheritance chain.

TObject
TBoldMemoryManagedObject   // inherited in framework

TBoldFlaggedObject                   // inherited in framework

TBoldSubscribableObject           // inherited in framework
TBoldElement                              // inherited in framework
TBoldDomainElement                 // inherited in framework
TBoldMember                             // inherited in framework
TBoldObject                                // inherited in framework
TBusinessClassesRoot                // Dummy
TAmObject                                 // basic info   
TAmStateObject                         // have states  

TPerson                                      // concrete class 

This is the inheritance tree for TPerson. Is it even possible to use a TAbstractPerson somewhere ?

18 hours ago, Ondrej Kelle said:

That's correct.

2 hours ago, David Schwartz said:

If you have circular references, then you need to re-think your design.

See https://stackoverflow.com/questions/53980032/how-to-avoid-using-inc-files-for-code-with-delphi for more details. 

But I now believe that interfaces is the correct solutions instead of direct references between the classes.

Ok so basically it is not possible to have direct references in both directions between two classes if they are stored in separate units...

I found http://docwiki.embarcadero.com/RADStudio/XE2/en/Classes_and_Objects#Forward_Declarations_and_Mutually_Dependent_Classes

I try to create 2 classes. Each of those have a reference to the other.

unit TestA;

interface

uses
  TestB;

type
//  TTestB = class;

  TTestA = class
  public
    M_TestB: TTestB;
  end;

implementation

end.

unit TestB;

interface

uses
  TestA;

type
  TTestB = class
    M_TestA: TTestA;
  end;
  
implementation

end.

Got

[DCC Error] TestA.pas(6): F2047 Circular unit reference to 'TestA'

What is wrong here ?

If I remove TestB from uses and add

TTestB = class;

I got this instead

[DCC Error] TestA.pas(9): E2086 Type 'TTestB' is not yet completely defined

Seems like links are not clickable https://github.com/mikerabat/mrmath

http://www.mrsoft.org/home/downloads.html

Look at https://stackoverflow.com/questions/4652958/is-there-a-way-to-log-every-gui-event-in-delphi. It try to intercept all events. Advantage is that you need much less modifications of your code. Disadvantage is that not all your methods is logged.

New book next year that could be interesting.

http://interpreter.analogmachine.org/

How can I get updates for new posts in this forum on the phone? With the old Google+ forum I used the Google app for that.