I have done some horrible code where I needed to know the following: If TSomeProc = procedure(....), then is it easy to determine or set entry vector of ThatProc: TSomeProc by stating ThatProc := @ProcWhereTheCodeLives_InTheCodeSegment;
It gets more difficult when you work with TSomeClassProc = procedure(....) of object, because two parts are referenced here: 1) The entry vector where the code lives, 2) The heap address where the object struct lives. (Known as the Self variable in a procedure of object) I have worked out which pointer of the two pointers belongs to the code and which to the instance with a trial. With a move operation, I was able to manipulate the two pointers, specifically to determine the address of the instance. The @ operator only gives you access to the procedure part. Is there, or will there be, another operator to give you access to the instance address? 2009/9/10 Mattias Gärtner <nc-gaert...@netcologne.de> > Zitat von Vincent Snijders <vsnijd...@vodafonevast.nl>: > > Jonas Maebe schreef: >> >>> >>> On 10 Sep 2009, at 14:01, Mattias Gärtner wrote: >>> >>> >>>>> Mattias Gärtner wrote: >>>>> >>>>>> Can someone explain why in mode objfpc comparing methods only compares >>>>>> the address, but not the instance? >>>>>> >>>>> >>>>> Seems perfectly logical to me (@ = Address of, in this case "code >>>>> address", the code is the same for all instances of a class). >>>>> >>>> >>>> OnClick:=...@myclick; >>>> >>>> The @ operator is more than "address of". >>>> >>> >>> The current behaviour has been there since svn revision 1, so it's quite >>> old and established at least (and Delphi/TP-compatible, afaik). >>> >> >> It is delphi compatible, not really intuitive, so I would welcome a change >> in the objfpc mode. >> >> See: >> http://bugs.freepascal.org/view.php?id=9228 >> http://bugs.freepascal.org/view.php?id=11868 >> > > To draw the whole picture: > > var a,b: TNotifyEvent; > > a=b compares only Code, not Data > a=nil compares only Data, not Code > Assigned(a) compares only Code, not Data > n.a. compares both > > I wonder how many programmers know this. > > Even the FCL contains code, where this leads to wrong code. > More important: I don't know a place, where a=b and a=nil are used right. > But I have seen a lot of code where it was used wrong. > > > Mattias > > > _______________________________________________ > fpc-devel maillist - fpc-devel@lists.freepascal.org > http://lists.freepascal.org/mailman/listinfo/fpc-devel >
_______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
