On Mon, Dec 18, 2017, at 05:23, Antoine Pitrou wrote:
> On Sun, 17 Dec 2017 21:07:02 -0500
> Random832 <random...@fastmail.com> wrote:
> >
> > Is there any practical for of having the flag off for one slot and on
> > for another slot that's been added later?
> >
> > Could this be replaced (that is, a slot for such a thing added before
> > it's too late) with a simple counter that goes up with each version, and
> > any "unused" slot should have NULL or some other sentinel value?
>
> Any replacement here would break binary compatibility, which is what
> those flags are precisely meant to avoid.
I meant replacing the mechanism for new fields, rather than existing ones.
> > If it
> > really is important to have the flags themselves, just add another set
> > of flags - Py_TPFLAGS_HAVE_MORE_FLAGS.
>
> Yes, we could... but it's more complication again.
Hmm, maybe that could be eased with macros...
/* Doing this preprocessor trick because if we used a ternary
* operator, dummy macros needed to prevent compile errors may
* become an attractive nuisance */
#define Py_TPFLAG_CHK(tp, flagname) \
Py__TPFCHK_##flagname(tp, flagname)
#define Py__TPFCHK_OLD(tp, flagname) \
((tp).tp_flags & Py_TPFLAGS_##flagname)
#define Py__TPFCHK_NEW(tp, flagname) \
((tp).tp_flags & Py_TPFLAGS_TPFLAGVER \
&& (tp).tp_flagver >= Py_TPFLAGVER_##flagname \
&& Py_TPFLAGCHK_##flagname(tp))
#define Py__TPFCHK_HEAPTYPE Py__TPFCHK_OLD
#define Py_TPFLAGS_HEAPTYPE (1UL<<9)
#define Py__TPFCHK_TPFLAGVER Py__TPFCHK_OLD
#define Py_TPFLAGS_TPFLAGVER (1UL<<31)
#define Py__TPFCHK_NEWFLD Py__TPFCHK_NEW
#define Py_TPFLAGVER_NEWFLD 32
#define Py_TPFLAGCHK_NEWFLD(tp) ((tp).tp_newfld != NULL)
So to check heap type you get Py_TPFLAG_CHK(tp, HEAPTYPE)
((tp).tp_flags & (1UL<<9))
And to check newfld1 you get Py_TPFLAG_CHK(tp, NEWFLD)
((tp).tp_flags & (1UL<<31) && (tp).tp_flagver >= 32 && ((tp).tp_newfld !=
((void *)0)))
Or in a "more flags" scenario:
#define Py__TPFCHK_NEW(tp, flagname) \
((tp).tp_flags & Py_TPFLAGS_TPMOREFLAGS \
&& (tp).tp_moreflag & PY_TPMOREFLAGS_##flagname)
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