use strict;
use warnings;

my %d = (
    foo => sub { "[@_]"; },
    bar => sub { "(@_)"; },
);

$_ = 'baz1';
s/(\w+)(??{!$d{$1}})/$d{$1}->($1)/ge; 
print "$_\n";

##</code><code>##

Use of uninitialized value in subroutine entry at line 10.
Can't use string ("") as a subroutine ref while "strict refs" in use at line 10.