[fpc-devel] Class field reordering

Michael Van Canneyt michael at freepascal.org
Sat Jul 14 14:26:32 CEST 2012

On Sat, 14 Jul 2012, Jonas Maebe wrote:

> On 14 Jul 2012, at 08:00, Martin Schreiber wrote:
>> On Saturday 14 July 2012 07:50:58 Martin Schreiber wrote:
>>> On Saturday 14 July 2012 01:44:39 Jonas Maebe wrote:
>>>> I've implemented an optimization that reorders the instance fields of
>>>> Delphi-style classes (and only of Delphi-style classes) to minimise
>>>> memory gaps caused by alignment differences and odd sizes. The effect
>>>> is the same as when you would change the order of the fields in the
>>>> source code to achieve this effect.
>>> I sometimes need "cracker" classes in MSEide and MSEgui to fix bugs and
>>> make extensinsions for FCL classes in order to access private fields
>>> (examples TDataset, TParam, TField, TFiler, TReader, TWriter, TComponent).
>>> Is it guaranteed that the local definitions have the same layout as the
>>> definition in the FCL unit?
> If you you use the same packrecords setting, yes (I doubt any such fcl units contain packrecords directives though, in which case they'll use the default).
>> Hmm, up to now I listed in the cracker classes fields up to the last private
>> field I need to access so the cracker classes would not brake by changing or
>> adding successive fields in the original classes. I assume now it is
>> necessary to always list all fields of the original class.
> If would you want to use that optimization, then yes. "Working around" the
> type system of the language is however generally asking for trouble,
> regardless of what reason you do it for.

Indeed. Maybe we can help by making some methods/properties protected ?


More information about the fpc-devel mailing list