[fpc-devel] Variant compiling errors

[petr.kristan at epos.cz]

On Mon, Oct 10, 2005 at 02:11:04PM +0200, Florian Klaempfl wrote:
> petr.kristan at epos.cz wrote:
> 
> > Hi.
> > 
> > After a few hours with gdb was isolated errors and strangeness in compiler 
> > at work with variants:
> > 
> > Example:
> > 
> > function c(const vv:  variant): variant;
> > begin
> >   result := vv;
> > end;
> > 
> > function b(vv:  variant): variant;
> > begin
> >   result := vv;
> > end;
> > 
> > function a(var vv:  variant): variant;
> > begin
> >   result := vv;
> > end;
> > 
> > procedure start;
> > var
> >   v, v1: Variant;
> > begin
> >   v := VarArrayCreate([0, 0], varVariant);
> > 
> >   a(v); 
> >   //if variant result of a() isn't assigned, fpc_finalize() at end of a(v)
> >   //destroys temporary result. But when start() ends fpc_finalize() tryes
> >   //to destroy it again
> > 
> >   b(v);
> >   //if b() is called then variant param is copied but not whole (deeply), vv.varray
> >   //points to the same place as v.array. At end of b(v) is pointer
> >   //vv.array destroyed by fpc_decref() and then v.array points to the
> >   //destroyed memory
> > 
> >   c(v);
> >   //At the start of func c() is v copied to the vv deeply but i think
> >   //that behaviour of "var" and "const" calling should be the same (by
> >   //reference) not vy value like c()
> > end;
> > 
> > I try to understand compiler code and repair it, but this is "very long
> > distance race". But like I see the responses to my previous reports
> > (absolutely no interest), this will be fastest solution :(. Really here
> > isn't anybody who understand to compiler code and help me with repair?
> > Or is anywhere another e-mail list or another comunication channel where
> > i can talk about this problem?
> > 
> > Petr
> > 
> 
> The var arrays problems are known, see also
> http://www.freepascal.org/bugs/showrec.php3?ID=3830
> 
> It requires some design changes though that's why it isn't fixed yet. The
> problem is that the compiler handles variants as ref. counted types when passing
> them as parameters etc. However, this is wrong behaviour as soon as a variant
> contains an array.
Thanks for explanation. Yesterday i looked at compiler code and fpc
internals documentation. I must recognize that fixing this is beyond my
strength. Is somebody working on it? I can help with debugging.
Vararray problem stopped my work -- porting big information system to fpc. 
In Rtl/fcl i can repair or fill missing, but here i'am helpless.
For that reason i hurry on fixing this.

Petr

-- 
Ing. Petr Kristan
.
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