breaking open a scalar with unpack P

[patcat88]

How kosher is the following code? Is it acceptable to break open a scalar like this? is this documented in Perl's documentation? how often is this done? Does printing of references to scalars always produce SCALAR(0XBABABABA)? is that documented? is a reference being a dualvar documented?

I was looking at the source code of Acme::ESP and I saw the module breaking open a scalar. The rest of the code I can't figure out due to a lack of parenthesis.

I wrote this script the test out if Acme::ESP was really breaking open the scalars or not.

I am aware this is not 64 compliant, although using 'J' in the right places should fix that.

$c = 'camel';
$ref =\$c;
print (($ref+0)."\n");
$ptr = pack( "L", $ref);
@a = unpack('LLLL',unpack('P16',$ptr));
$flags = $a[2];
$h{'SVf_IOK'} = 0x00000100;   # has valid public integer value */
$h{'SVf_NOK'} = 0x00000200;   # has valid public numeric value */
$h{'SVf_POK'} = 0x00000400;   # has valid public pointer value */
$h{'SVf_ROK'} = 0x00000800;   # has a valid reference pointer */

$h{'SVp_IOK'} = 0x00001000;   # has valid non-public integer value */
$h{'SVp_NOK'} = 0x00002000;   # has valid non-public numeric value */
$h{'SVp_POK'} = 0x00004000;   # has valid non-public pointer value */
$h{'SVp_SCREAM'} = 0x00008000;   # has been studied? */
$h{'SVphv_CLONEABLE'} = 0x00008000;   # PVHV (stashes) clone its objec
+ts */
$h{'SVpgv_GP'} = 0x00008000;   # GV has a valid GP */
$h{'SVprv_PCS_IMPORTED'} = 0x00008000;   # RV is a proxy for a constan
+t
                       #subroutine in another package. Set the
                       #CvIMPORTED_CV_ON() if it needs to be
                       #expanded to a real GV */

$h{'SVs_PADSTALE'} = 0x00010000;   # lexical has gone out of scope */
$h{'SVpad_STATE'} = 0x00010000;   # pad name is a "state" var */
$h{'SVs_PADTMP'} = 0x00020000;   # in use as tmp */
$h{'SVpad_TYPED'} = 0x00020000;   # pad name is a Typed Lexical */
$h{'SVs_PADMY'} = 0x00040000;   # in use a "my" variable */
$h{'SVpad_OUR'} = 0x00040000;   # pad name is "our" instead of "my" */
$h{'SVs_TEMP'} = 0x00080000;   # string is stealable? */
$h{'SVs_OBJECT'} = 0x00100000;   # is "blessed" */
$h{'SVs_GMG'} = 0x00200000;   # has magical get method */
$h{'SVs_SMG'} = 0x00400000;   # has magical set method */
$h{'SVs_RMG'} = 0x00800000;   # has random magical methods */

$h{'SVf_FAKE'} = 0x01000000;   # 0: glob or lexical is just a copy
                       #1: SV head arena wasn't malloc()ed
                       #2: in conjunction with SVf_READONLY
                      #marks a shared hash key scalar
                      #(SvLEN == 0) or a copy on write
                      #string (SvLEN != 0) [SvIsCOW(sv)]
                       #3: For PVCV, whether CvUNIQUE(cv)
                #      refers to an eval or once only
                #      [CvEVAL(cv), CvSPECIAL(cv)]
                #       4: Whether the regexp pointer is in
                #      fact an offset [SvREPADTMP(sv)]
                #       5: On a pad name SV, that slot in the
                #      frame AV is a REFCNT'ed reference
                #      to a lexical from "outside". */
$h{'SVphv_REHASH'} = 0x01000000;     # 6: On a PVHV, hash values are b
+eing
                      #recalculated */
$h{'SVf_OOK'} = 0x02000000;   # has valid offset value. For a PVHV thi
+s
                       #means that a hv_aux struct is present
                       #after the main array */
$h{'SVf_BREAK'} = 0x04000000;   # refcnt is artificially low - used by
                       #SV's in final arena cleanup */
$h{'SVf_READONLY'} = 0x08000000;   # may not be modified */

foreach(keys %h) {
     print "matched $_\n" if ($flags & $h{$_});
}
print 'string depointered "'.unpack('P6',pack('L',$a[3])).'"'."\n";