You missed one part of the trick. The body of an lvalue sub doesn't get executed when it is used as an lvalue. The trick works only if the last expression is an lvalue (as is trinary op). That means you do no good to shift in or copy the function arguments. $key and $self in your example are undefined when called as an lvalue.

Arguments are still usable, but you need to initialize them in the last line of the sub. Here's a minimal rewrite. 

sub get_set :lvalue {
    my $junk;
    key_ok( $_[1] ) ? $_[0]->{ $_[1] } : $junk;
}

[download]
Note that $junk is effectively a package global variable holding the last value assigned with a not-ok $key. You can retrieve it with $foo->get_set($bad_key), but the value returned is for any $foo of the class.

After Compline,
Zaxo

In reply to Re: Experimenting with Lvalue Subs by Zaxo
in thread Experimenting with Lvalue Subs by Limbic~Region

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