And just to fool around with the above code, the following example emphasizes the previous point that what matters is the current value of the global $_ when the anonymous sub runs, not its value at its time of creation. Whereas with the lexical version, what matters is the value of lexical $i at time of creation

my (%withlex, %withglobal);

for (1 .. 10) {
   my $ref = sub { return $_ };
   $withglobal{$ref} = $ref;
   print $ref->(), "\n";
}
print keys %withglobal;
print "\n";

$_ = 'foo';
foreach my $key ( keys %withglobal ) {
    print "k: $key\tv: ", &{ $withglobal{$key} }(), "\n";
}

for my $i (1 .. 10) {
   my $ref = sub { return $i };
   $withlex{$ref} = $ref;
   print $ref->(), "\n";
}
print sort { $withlex{$a} <=> $withlex{$b} } keys %withlex;
print "\n";

my $i = 'bar';
foreach my $key ( sort { $withlex{$a} <=> $withlex{$b} } keys %withlex
+ ) {
    print "k: $key\tv: ", &{ $withlex{$key} }(), "\n";
}

print "Using lex num of subs is " . (keys %withlex) . "\n";
print "Using global num of subs is " . (keys %withglobal) . "\n";
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