Interestingly, reftype only checks the length of ref, which is why it can probably be fooled by "\0".

You are looking at the perl implementation, which isn't quite what i would consider to the canonical implementation. IMO the canonical implementation is the XS one:

char *
reftype(sv)
    SV * sv
PROTOTYPE: $
CODE:
{
    if (SvMAGICAL(sv))
    mg_get(sv);
    if(!SvROK(sv)) {
    XSRETURN_UNDEF;
    }
    RETVAL = sv_reftype(SvRV(sv),FALSE);
}
OUTPUT:
    RETVAL
[download]

In Data::Dump::Streamer its implemented as

char *
reftype(sv)
    SV * sv
PROTOTYPE: $
CODE:
{
    if (SvMAGICAL(sv))
    mg_get(sv);
    if(!SvROK(sv)) {
    XSRETURN_NO;
    } else {
        RETVAL = sv_reftype(SvRV(sv),FALSE);
    }
}
OUTPUT:
    RETVAL
[download]

Notice the only difference is the XSRETURN_NO; versus XSRETURN_UNDEF;. With the benefit of experience IMO the use of XSRETURN_UNDEF; was a mistake. I've said as much on p5p a number of times, but without much response. I guess it would be too dangerous a change, which is why im going to be providing patches to implement _reftype() so you can say

if (_reftype($foo) eq $TYPE) { ... }
[download]

without worrying about warnings. Of course if you don't want to wait, you can always

use Data::Dump::Streamer qw(reftype);
[download]

And get the more practical implementation Right Now. :-)

Unfortunately, Data::Dump::Streamer is 5.6+ (though you don't have a "use 5.006;" line before your "use warnings;" line). This came up in the context of me helping JHUCKABY with DBM::Deep and I want to keep DBM::Deep able to run with older Perls.

It seems sad, though, that reftype() won't be patched to XSRETURN_NO, especially as that makes more sense. Also, why can't the Perl version be patched to at least return !!0 instead of explicit undef?

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My criteria for good software:

1. Does it work?
2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

It seems sad, though, that reftype() won't be patched to XSRETURN_NO, especially as that makes more sense. Also, why can't the Perl version be patched to at least return !!0 instead of explicit undef?

XSRETURN_NO is how you do return !!0 in XS.

And the answer I think is here:

D:\dev\>perl -e"print defined !!0"
1
[download]

But Im hopeful that the p5p powers that be will be receptive of the idea of a _reftype() sub that returns PL_no instead of Pl_undef. (Which is what XSRETURN_NO and XSRETURN_UNDEF do.)

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$world=~s/war/peace/g