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Postings from August 2011
On Fri, Aug 12, 2011 at 9:20 PM, Chip Salzenberg <rev.chip@gmail.com> wrote:
> /me lights the Tim Toady Signal
> (I don't think this bug goes back that far, but I want to understand the design principles involved)
Turns out it does go back that far. But in this diving, I confess
I've gained a measure of empathy for Larry's plaintive cry: "What have
you done to my program?!"
First, the earliest ancestor of mg_get() did not play with the OK flags.
This is 5.0 alpha 2, and oh how simple it all started:
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 14) int
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 15) mg_get(sv)
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 16) SV* sv;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 17) {
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 18) MAGIC* mg;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 19) for (mg =
SvMAGIC(sv); mg; mg = mg->mg_moremagic) {
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 20) MGVTBL* vtbl =
mg->mg_virtual;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 21) if (vtbl &&
vtbl->svt_get)
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 22)
(*vtbl->svt_get)(sv, mg);
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 23) }
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 24) return 0;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 25) }
A subsequent revision introduced the first public/private flag games.
Here is 5.0 alpha 4 (463ee0b2):
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 14) int
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 15) mg_get(sv)
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 16) SV* sv;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 17) {
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 18) MAGIC* mg;
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 19)
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 20) SvMAGICAL_off(sv);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 21) SvFLAGS(sv)
&= ~(SVf_IOK|SVf_NOK|SVf_POK);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 22) SvFLAGS(sv)
|= SvPRIVATE(sv) & (SVf_IOK|SVf_NOK|SVf_POK);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 23) SvPRIVATE(sv)
&= ~(SVf_IOK|SVf_NOK|SVf_POK);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 24)
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 25) for (mg =
SvMAGIC(sv); mg; mg = mg->mg_moremagic) {
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 26) MGVTBL* vtbl =
mg->mg_virtual;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 27) if (vtbl &&
vtbl->svt_get)
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 28)
(*vtbl->svt_get)(sv, mg);
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 29) }
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 30)
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 31) SvMAGICAL_on(sv);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 32) SvPRIVATE(sv)
&= ~(SVf_IOK|SVf_NOK|SVf_POK);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 33) SvPRIVATE(sv)
|= SvFLAGS(sv) & (SVf_IOK|SVf_NOK|SVf_POK);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 34) SvFLAGS(sv)
&= ~(SVf_IOK|SVf_NOK|SVf_POK);
463ee0b2 (Larry Wall 1993-11-10 00:00:00 +0000 35)
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 36) return 0;
79072805 (Larry Wall 1993-10-07 23:00:00 +0000 37) }
So even at this very early date, after mg_get() one could not depend
on having any meaningful OK flags. And from this time the details may
have changed (a lot!), this aspect of the flags has remained constant.
Which leaves the question still unanswered: How has this ever worked?
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