[fpc-devel] Another question about class vars

Birger Jansen birger at cnoc.nl
Thu Nov 4 12:58:41 CET 2010

Hi all,

I am still a little confused about class vars and the difference there seems to be with how this behaves in Delphi. Take the following class:

  TMyClass = class
    class var SomeClassVar: Integer;
    SomeVar: Integer;

And two instances of this class: a,b: TMyClass

And let's do this:

  a.SomeClassVar := 10;
  b.SomeClassVar := 20;
  a.SomeVar := 30;
  b.SomeVar := 40; 

I would expect this results:

 a.SomeClassVar    = 20
 b.SomeClassVar    = 20
 a.SomeVar         = 30
 b.SomeVar         = 40

But it turns out that for both a and b the value for SomeVar = 40. Which leads to the conclusion that SomeVar is also a class var. I would think that because of the new section (public) the declaration would default to 'var', but it doesn't. SomeVar is also added as a class var.

Changing the class to this...

  TMyClass = class
    class var SomeClassVar: Integer;
    var SomeVar: Integer;

(adding var to SomeVar)

...gives the expected result. I know this is probably not a bug, as was explained to me in my last post with a question related to class vars. But this minuscule difference between Delphi and FPC has a great impact (just spend 4 hours on tracking an issue down to this).

Any chance that this behaviour can be changed or is it just me who should be more carefull with this?

Kind regards,

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