Re: Dualvars besides $!

[ikegami]

This post is wrong.

---

Whether the docs are correct or not depends on the version of Perl.

perl -MDevel::Peek -e'$!=1; print("$!\n"); Dump($!);'

5.8.9:

...
  FLAGS = (GMG,SMG,pNOK,pPOK)
...

No public values. Not a dualvar.

5.18.1:

...
  FLAGS = (GMG,SMG,NOK,POK,pNOK,pPOK)
...

Two public values (NOK = has NV = has floating point number, POK = has PV = has string). Dualvar.

[ikegami]

The latest Scalar::Util::isdual considers FLAGS = (GMG,SMG,pNOK,pPOK) to be a dualvar. (No idea about earlier versions, but I suspect it's the same.) The docs are wrong. The following returns 1 for both 5.8.9 and 5.18.1, while the docs say it returns false:

perl -MScalar::Util=isdual -MDevel::Peek \
   -e'$!=1; print("$!\n"); print(isdual($!)?1:0,"\n"); Dump($!);'

Nit: $! is magical (like tied variables), but it's not a tied variable like the docs say.