I'm attempting to port GExperts from Delphi to Lazaurus and noticed the definition of TPropInfo differs from Delphi's.

In FPC's TPropInfo the PropType field is PTypeInfo whereas in Delphi it is PPTypeInfo. I'm not sure what is actually gained by this extra level of indirection but it exists none the less.

Are there any plans to update TPropInfo to be compatible with Delphi or do
I need to  wrap dependent code with compiler conditionals?

There are no plans as we have to stay compatible with our own old codebases as well. You'll need to use compiler conditionals.

Regards,
Sven

2014-05-31 11:48 GMT+02:00 Sven Barth :

I think it is possible to write code without $ifdef (valid for Delphi and FPC) if you use the typeinfo unit to extract the information. http://www.freepascal.org/docs-html/rtl/typinfo/

Vincent

No, that is exactly the point. Compare the declaration of TPropInfo in Delphi and FPC:

http://docwiki.embarcadero.com/Libraries/XE3/en/System.TypInfo.TPropInfo http://www.freepascal.org/docs-html/rtl/typinfo/tpropinfo.html

In Delphi you have PropType as PPTypeInfo while in FPC you have PTypeInfo.

Regards,
Sven

By Barry Kelly in comment :) :

http://stackoverflow.com/questions/3443097/what-is-the-identity-pointer-before-a-ttypeinfo-there-for

"all typeinfo fixups - pointers from one blob of typeinfo to another - are of type PPTypeInfo, not PTypeInfo, to handle the dynamic linking case. In the case of static linkage, there needs to be an intermediate pointer for the convention to work, and part of the typeinfo itself makes as much sense as any. That is to say, it's not there for the linker; it's there because of the convention, and the convention is there because of dynamic linking, which is done the way it is to maximize potential for page sharing."

Regards,
Maciej Izak (hnb)

In our previous episode, Maciej Izak said:

Thanks, I added it to the wiki:

http://wiki.freepascal.org/packages#Details

Vincent Snijders wrote

I think it is possible to write code without $ifdef (valid for Delphi and FPC) if you use the typeinfo unit to extract the information. http://www.freepascal.org/docs-html/rtl/typinfo/

Almost, but not quite. Good news is, it is not nearly as bad as Sven makes it out to be.

The tiOPF project uses RTTI extensively. I have written a lot of that code, and with the following helper function, I could eliminate a lot of IFDEF's between FPC and Delphi RTTI behaviour.

function tiGetTypeInfo(PropInfo: PPropInfo): PTypeInfo;
begin
{$IFDEF FPC}
  Result := PropInfo^.PropType;
{$ELSE}
  Result := PropInfo^.PropType^;
{$ENDIF}
end;

I've also introduced an enhanced GetPropInfo() with a signature as follows:

function tiGetPropInfo(AClass: TClass; PropPath: string; PInstance:
Pointer): PPropInfo;

To see the complete code, take a look at the Core/tiRTTI.pas unit in the tiOPF's 'tiopf2' branch.

That unit is also fully unit tested. Tests and usage examples can be found in the following unit:

UnitTests/Tests/tiRTTI_TST.pas

Regards,
- Graeme -

Am 03.06.2014 10:26 schrieb "Graeme Geldenhuys" <

If one uses a helper function like you did then it's indeed not as bad, but if one doesn't...

Out of curiosity: is this helper declared as "inline"? Would get rid of the call completely in both Delphi and FPC...

I've also introduced an enhanced GetPropInfo() with a signature as

follows:

function tiGetPropInfo(AClass: TClass; PropPath: string; PInstance: Pointer): PPropInfo;

Might also profit from a declaration as "inline" :)

Yours,
Sven

Sven Barth wrote

If one uses a helper function like you did then it's indeed not as bad, but if one doesn't...

Indeed. :) I find it is often amount managing readability of code. The application developer doesn't need to worry to much about the difference between platforms - if you give them the right tools. After all, that is what FPC is all about.

Out of curiosity: is this helper declared as "inline"? Would get rid of the call completely in both Delphi and FPC...

A very good suggestion thanks. I'll apply that immediately.

This one might not work as inline, as it is much more involved. Also note the PropPath property. tiOPF can handling calls like:

tiGetPropInfo(MyObject, 'Contact.Address.PostCode', ...)

It will iterate through the MyObject.Contact.Address.PostCode properties, obviously doing NULL checks along the way. Hence the name "PropPath" (property path).

Regards,
- Graeme -

Ah ok. I thought it was also a more simpler wrapper call. Then not :P

Regards,
Sven

I have the feeling that the introduction of dynamic packages in FPC *will* require us to change our current RTTI from PTypeInfo to PPTypeInfo... :/

Regards,
Sven

So better to do it earlier rather than later ;P

Regards,
Maciej Izak (hnb)