Hi!

How can I access an inherited inherited method which was overloaded?

====== Example: ======

{$mode objfpc}{$H+}
Program TestInherited;
Uses Classes, SysUtils;
Type
  TFirst = class
    Constructor Create(A,B,C:Integer);
  End;
  TSecond = class(TFirst)
    Constructor Create(A,B:Integer);
  End;
  TThird = class(TSecond)
    Constructor Create(A,B:Integer);
  End;
Constructor TFirst.Create(A, B, C: Integer);
Begin
  { ... }
End;
Constructor TSecond.Create(A, B: Integer);
Begin
  inherited Create(A,B,0);
End;
Constructor TThird.Create(A, B: Integer);
Begin
  inherited Create(A,B,0);   { <-- Error: Wrong number of parameters specified for call to "Create" }
End;
Begin
End.

===================================

The compiler complains in TThird.Create that the call to the inherited method doesn't work. Removing the word "inherited" doesn't help.

What happened to the method with 3 parameters? Why is there an error message? How can I access it?

Thanks
Hansi

Johann Glaser wrote

Hi! How can I access an inherited inherited method which was overloaded?

AFAIK TThird inherits Create method not from TFirst, but from TSecond, i.e. TThird.Create calls TSecond.Create, not TFirst.Create.

Johann Glaser wrote

How can I access an inherited inherited method which was overloaded?

You can't, one of them will need to have a different name.

Joao Morais

try (but i not like it )

begin
  TFirst(Self).Create(A, B, 0);
end;

Hi!

Joao Morais wrote

Johann Glaser wrote: > How can I access an inherited inherited method which was overloaded? You can't, one of them will need to have a different name.

Thanks.

Why is a method hidden, just because it has the same name? Isn't it a totally different method, because it has different parameters? Then it should be visible. Or did I miss something?

Bye
Hansi

Well, afaik you cannot overload methods which belongs to different classes, even if one inherits from the other. Otoh, note that the Zaher's tip should work very well.

Imho a better approach is change the constructor name if you _really_ need to use two incompatible params list. Even better would be creating constructors with the same syntax. You can use default parameters to accomplish this.

Joao Morais

Johann Glaser wrote

Hi! How can I access an inherited inherited method which was overloaded?

Try the following, mark the constructors as overloaded:

     Constructor Create(A,B,C:Integer); overload;

End; TSecond = class(TFirst)

     Constructor Create(A,B:Integer); overload;

End; TThird = class(TSecond)

      Constructor Create(A,B:Integer); overload;

The constructor with 3 parameters is hidden.

Vincent

Hi!

Thanks, that really helped now. While Zaher Dirkey's hint (Mon, 4 Aug 2008 15:24:03 +0300) also helped and did it's job, it had one drawback: If TFirst.Create raised an exception, this could not by caught by TThird.Create. Even worse, it "converted" to an "Access violation" exception.

I debugged this issue and found that it happend at a "call 0x30(%ecx)" instruction in TThird.Create. ECX pointed to a memory structure where address 0x30 was $00000000. This seems very likely to be a problem with internals of FPC's handling of constructors and exceptions.

Using "overload" now works like a charm. Michael, could you please add this to the documentation?

Thanks
Hansi