[fpc-devel] RFC: customvariant handling in variants.pp and fmtbcd.pp

[Sergei Gorelkin]

LacaK пишет:
> 
> I can fix it by following fixs:
> 
> 1. fmtbcd_castto.diff ... added case when castto varString is requested 
> ... then do not use cast throught varDouble (to avoid lost of 
> precision), but convert directly from TBCD to string
> 
> 2. variants.pp ... here we must add handling of customvariants into 
> sysvartolstr ... I created "helper" function TryCastFromCustomVariant
> which can be used multiple times (now in sysvartolstr and sysvartoreal) 
> ... I isolate in this function code which is required multiple times.
> 
> I am not sure if
> 1. is this optimal approach, or is better to put same code repeatedly in 
> sysvartolstrm sysvartoreal and in future in others sysvarto... ?
> 2. is the name and place of such function good choosen ?
> 
Doing what you propose isn't good. Checking for custom variant type is expensive because it involves 
locking, therefore custom variant handling should be done *after* the standard types.
The real problem is that the standard types are currently handled in VarUtils.VariantToX functions, 
which do not depend on Variants unit and cannot use custom variant stuff.

The correct solution would be to move the code of VariantToX functions to Variants unit, inlining 
them to sysvartoX functions. But if you try that, you'll discover very soon that VariantChangeTypeEx 
(non-Windows implementation in varutils.inc) depends on some of them. This is again not correct, 
because conversion functions called from VariantChangeTypeEx do not need to handle Pascal-specific 
types and by-reference variants. But a simplifed portion of conversion functions have to stay in 
VarUtils unit.

This is of course a major rewrite, but I'd stay on it, because with a number of quick-fixes we risk 
to end up with unmaintainable code.

Regards,
Sergei