How about always accepting the arguments as an array?

sub instantiator {
    my @state = @_;
    sub {
        # work on @state
    }
}
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I think that working on @_ gives you less of a closure than you suggest.

To retain a data structure through the argument list of a sub, you need to pass a reference to it (you knew that!). Then you can do a perly case switch on ref $_[0] to return a sub specialized to the argument type.