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MyBase during create? (inheritance)

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  • MyBase during create? (inheritance)

    I am trying to set a property from the inherited class:
    Code:
        Class Method Create
             MyBase.ID = 1234
        End Method
    I get:
    PowerBASIC for Windows
    PB/Win Version 9.01
    Copyright (c) 1996-2009 PowerBasic Inc.
    Venice, Florida USA
    All Rights Reserved

    Error 596 in C:\.............
    (33:009): Inherited interface expected
    Line 33: MyBase.ID = 1234
    Is there a simple workaround?
    Now it seems i need to call an initialization method first..
    hellobasic

  • #2
    Classes (aka class methods) do not inherit other interfaces, only interfaces inherit other interfaces. Just like you said, you probably need a Init method in an interface that inherits this other interface.
    Sincerely,

    Steve Rossell
    PowerBASIC Staff

    Comment


    • #3
      Thank you.
      hellobasic

      Comment


      • #4
        Though, i have this serious design issue.

        The base class maintains a handle.
        The destroy is never executed so the handle remains open.

        The 'inheritance class''s destroy is also not able to call some kind of 'dispose' method in the base class's interface.

        Since i will have hundreds of inheritance classes i can not embed them in the same base class.

        Any idea to destroy the handle in the base class when the inh. class get's unloaded?

        Thanks,
        hellobasic

        Comment


        • #5
          Edwin,
          I'm not sure what you are trying to do but it may be a faulty design decision.
          Do not look at Pb Classes as you would c++,java,c#. Look at it more as COM with a bit of extras. COM has no inheritance so it may help to look at your design problems from that aspect first, then see if you can use the extras.

          In a number of situations I decided against inheritance and used containment instead.

          James

          Comment


          • #6
            It may be an incorrect design.
            The base class must do all code except the few Override functions.
            But the base class constructor/destructor is never executed and i am not sure if this is an implementation issue or simply undesired behaviour.
            The overrides should make it easy for me and let the base maintain it's instance variables.

            Here is an example, the brush handle remains 0.
            I know solvable but that implies more code.
            Better to investigate now than a rebuild for 2 or 300(!) classes

            Code:
            Class Class1
            
                Instance m_Handle As Long
            
                Class Method Create
            
                    MsgBox "Class1 Method Create"
                    m_Handle = CreateSolidBrush( 0 )
            
                End Method
            
                Class Method Destroy
                    MsgBox "Class1 Method Destroy"
                End Method
            
                Interface Interface1: Inherit IUnknown
            
                    Property Get Handle() As Long
                        Property = m_Handle
                    End Property
            
                End Interface
            
            End Class
            
            Class Class2
            
                Interface Interface2: Inherit Class1, Interface1
            
            '        Override Property Get Handle() As Long
            '            Property = MyBase.Handle            
            '        End Property
            
                End Interface
            
            End Class
            
            Function TEST() As Long
            
                Local o As Interface2
                o = Class "Class2"
                
                MsgBox Str$( o.Handle )     
            
            End Function

            Added: i forgot the deleteobject() in the destroy.
            hellobasic

            Comment


            • #7
              Call MyBase.Create

              It's a little bit of code but call the base class constructor.

              Code:
              ...
              
              Class Class2
                  
                  Class Method Create()
                      ' Call parent object constructor
                      mybase.create
              
                      ' Do class 2 stuff here
              
                  End Method
              
              ...
              If there is a constructor of the class, the base class constructor may be overridden. It should be the responsibility of the developer to call the base class constructor, if necessary. It should be first, called before any other code is done in the class 2.

              It would be nice if the base class constructor was automatically called if the child/sub class had no constructor defined. In other words, MyBase.Create called automatically if a Constructor was not written. This process occurs in other OOP languages. Should this already be happening? Should this be reported as a bug or a request?

              Comment


              • #8
                Oh boy, that does work!
                I thought that Mybase couldn't be used in the class method of the inh. class.
                But that restriction applies to the int. members..

                Yes, it would be nice if PB invoked the base class.

                Note that any other class method can not be invoked this way.
                Only Create and Destroy are accepted.
                (Maybe a logical restriction since this is a vtable system)
                hellobasic

                Comment


                • #9
                  It would be nice if the base class constructor was automatically called if the child/sub class had no constructor defined. In other words, MyBase.Create called automatically if a Constructor was not written. This process occurs in other OOP languages. Should this already be happening? Should this be reported as a bug or a request?
                  As I said previous this is NOT other oop languages and is not a bug. I really see no reason for it when you can just call MyBase.Create? There may be instances where you don't want the base class create called.

                  James

                  Comment


                  • #10
                    Originally posted by jcfuller View Post
                    As I said previous this is NOT other oop languages and is not a bug. I really see no reason for it when you can just call MyBase.Create? There may be instances where you don't want the base class create called.

                    James
                    If a constructor isn't created, PB could generate one with a call to MyBase.Create.

                    If a constructor exists, PB doesn't generate one. Developer must call MyBase.Create in the created constructor if wanted.

                    With generation of a default constructor typing and clutter of code would be saved. It would also prevent bugs where the developer forgets to initialize (call the base constructor) in sub classes.

                    There is no reason why PB should not do this. One could write a constructor if the developer wanted to explicitly show it is being called.

                    Comment


                    • #11
                      Actually, not true. The very good reason is that you may not want CREATE called in the inherited class.

                      Comment


                      • #12
                        >There may be instances where you don't want the base class create called.
                        Imo not (never) and then.. an easy override, just a matter of logical programming imo.
                        hellobasic

                        Comment


                        • #13
                          Sorry for coming back on this.
                          I still would like to find me a way to call the inherit class from the base class.
                          It may not be possible..., if i just could reach the object from inside the baseclass i would be fine.
                          I already understand the comparison may not do but this is somewhat what i need:

                          (Baseclass)
                          Code:
                          using System;
                          using System.Collections.Generic;
                          using System.Text;
                          
                          abstract class Class1
                          {
                              public abstract string GetABC(int colIndex);
                          
                              public string GetXYZ(int colIndex)
                              {
                                  return GetABC(colIndex);
                              }
                          }
                          The class to use:
                          Code:
                          using System;
                          using System.Collections.Generic;
                          using System.Text;
                          
                          class Class2 : Class1
                          {
                              public override string GetABC(int colIndex)
                              {
                                  switch (colIndex)
                                  {
                                      case 1:
                                          return "abc";
                                      case 2:
                                          return "def";
                                  }
                                  return "";
                              }
                          }
                          Being called like:
                          Code:
                                  private void button1_Click(object sender, EventArgs e)
                                  {
                                      Class2 c = new Class2();
                                      MessageBox.Show( c.GetXYZ(1));
                                  }
                          The conclusion for com was that i may need to initialize but there is no automated moment to do so (this is actually what i am asking here).
                          Unless you run the init call by testing a variable and place this line in every call.
                          Call's not being overridden will never initialize.

                          Conclusion(?):
                          This means right after create i must call an initialize.
                          (But that wouldn't be an automated call then)
                          hellobasic

                          Comment

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