> combined getter/setter ... Return the value when called without an additional arg,

from my experience are mutators written in a way to always return the value.

> A call with an undefined arg clears the attribute - just like in my example.

OK ... but in that case why do you have a default value at all?

Anyway, if you want to allow to set to undef and don't wanna introspect @_ , then you're stuck in a kind of semipredicate problem.

Such problems can be solved in Perl by setting a new "impossible"° object MISSING as default, like

use constant MISSING => bless {}, "MyPackg::__Missing__"

and later

sub mutator ($value = MISSING) { ...BODY... }

(untested)

If you see that an arguments equals to that "impossible" value blessed into your own private namespace below "MyPackg", you can be sure that it wasn't used by accident.

HTH! :)

update

clearer rewording, clearer code

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

°) of course it's possible that such a value is used, but extremely unlikely without intend.

In reply to Re^3: Distinguish between missing and undefined arguments with subroutine signatures (semipredicate problem) by LanX
in thread Distinguish between missing and undefined arguments with subroutine signatures by jo37

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