Re: [fpc-pascal] Interfaces inheritance and Supports routine

2008-11-03 Thread Michael Van Canneyt 


On Sun, 2 Nov 2008, Graeme Geldenhuys wrote:

 On Sun, Nov 2, 2008 at 6:31 PM, Vladimir Zhirov [EMAIL PROTECTED] wrote:
  So the questions are:
  1) Is this an expected behavior?
  2) Are there any detailed documentation to read on this subject? I have
  not found anything, Supports is not very google-friendly name :(
 
 http://dn.codegear.com/article/29779
 
 From this article it seems things have changed since Delphi 8 onwards.
  The last Delphi version I used was D7. :-)  I don't know what delphi
 version FPC's features are based on.

D5 or D7.

All Delphis between D7 and D2007 were not real Delphis :-)

Michael.
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[fpc-pascal] Interfaces inheritance and Supports routine

2008-11-02 Thread Vladimir Zhirov 
Hi,

I've got a question on how does Supports function work. Here is the
quote from the FPC docs:

 Check whether a class or given interface supports an interface.
 Supports checks whether Instance supports the interface identified by IID. It 
 returns True
 if it is supported, False. Optionally, a pointer to the interface is returned 
 to Intf.

Suppose I have the code like this:

 IMyBasicInterface = interface
  ['{B6F77975-0C46-4B09-9682-CE96C4CA465A}']
  procedure DoSomething;
 end;

 IMyExtendedInterface = interface(IMyBasicInterface)
   ['{DF214D0F-7B92-487F-B21A-4698B1E044AC}']
   procedure DoSomethingElse;
 end;

 TMyClass = class(IInterfacedObject, IMyExtendedInterface)
   procedure DoSomething;
   procedure DoSomethingElse;
 end;

 var
   MyClassInstance: TMyClass;

The following call returns True as expected:
 Supports(MyClassInstance, IMyExtendedInterface);

But this one returns False, that seems strange for me:
 Supports(MyClassInstance, IMyBasicInterface);

Supports does not seem to take into account interfaces inheritance,
so to make the second call work as expected, I have to change TMyClass
declaration to

 TMyClass = class(IInterfacedObject, IMyBasicInterface, IMyExtendedInterface)

So the questions are:
1) Is this an expected behavior?
2) Are there any detailed documentation to read on this subject? I have
not found anything, Supports is not very google-friendly name :(

Thanks in advance.

---
Vladimir.

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Re: [fpc-pascal] Interfaces inheritance and Supports routine

2008-11-02 Thread Graeme Geldenhuys 
On Sun, Nov 2, 2008 at 6:31 PM, Vladimir Zhirov [EMAIL PROTECTED] wrote:

 Supports does not seem to take into account interfaces inheritance,
 so to make the second call work as expected, I have to change TMyClass
 declaration to

 TMyClass = class(IInterfacedObject, IMyBasicInterface, IMyExtendedInterface)

 So the questions are:
 1) Is this an expected behavior?


I'm not an expert with Interfaces, but as far as I understood the
documentation and from what I have seen in other code, that is
expected behaviour.  Below is information from the Kylix 3 help:

---[ kylix 3 help ]-

 An interface-type expression cannot reference an object whose class
implements a descendant interface, unless the class (or one that it
inherits from) explicitly implements the ancestor interface as well.

For example,
type
  IAncestor = interface
  end;
  IDescendant = interface(IAncestor)
procedure P1;
  end;
  TSomething = class(TInterfacedObject, IDescendant)
procedure P1;
procedure P2;
  end;
  ...
var
  D: IDescendant;
  A: IAncestor;
begin
  D := TSomething.Create;  // works!
  A := TSomething.Create;  // error
  D.P1;  // works!
  D.P2;  // error
end;

In this example,
 A is declared as a variable of type IAncestor. Because TSomething
does not list IAncestor among the interfaces it implements, a
TSomething instance cannot be assigned to A. But if we changed
TSomething's declaration to
TSomething = class(TInterfacedObject, IAncestor, IDescendant)
 ...the first error would become a valid assignment.
---[ end ]-


Regards,
  - Graeme -


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Re: [fpc-pascal] Interfaces inheritance and Supports routine

2008-11-02 Thread Graeme Geldenhuys 
On Sun, Nov 2, 2008 at 6:31 PM, Vladimir Zhirov [EMAIL PROTECTED] wrote:
 So the questions are:
 1) Is this an expected behavior?
 2) Are there any detailed documentation to read on this subject? I have
 not found anything, Supports is not very google-friendly name :(

http://dn.codegear.com/article/29779

From this article it seems things have changed since Delphi 8 onwards.
 The last Delphi version I used was D7. :-)  I don't know what delphi
version FPC's features are based on.


Regards,
  - Graeme -


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