Yes - when you descend to that level they become very similar, indeed :-)

At a high level:
validate $xdefined &$xref $x && defined &$x
code refreturns resultreturns resultreturns result
sub namediesreturns resultreturns false
other refsdiesdiesdies
undefined?stringifiedreturns false

I couldn't even get correct results on perl-5.6.2 with CvROOT and CvXSUB

That's odd, because defined and sub calls use CvROOT(cv) || CvXSUB(cv) in 5.6.2 as well.

In reply to Re^6: How do I test the validity of a CODE reference? by ikegami
in thread How do I test the validity of a CODE reference? by pilap

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