There does look like one possibility. Perlguts mentions that with Perl 5.16 and earlier: Copy-on-write (see the next section) shared a flag bit with read-only scalars. So the only way to test whether sv_setsv , etc., will raise a "Modification of a read-only value" error in those versions is: SvREADONLY(sv) && !SvIsCOW(sv)

Scalar::Util doesn't do anything special for 5.16 or earlier, so it could have false positives in that case. Of course, 5.18 (where it's fixed) was released in 2013 :)

In reply to Re^4: How could I check if a variable is 'read-only'? by kschwab
in thread How could I check if a variable is 'read-only'? by vladb

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