use Benchmark;

my $size = 100000;
my %hash1 = map { $_ => 1 } (0..$size);
my %hash2 = map { $_ => 1 } ($size..(2*$size));
my $t0 = new Benchmark;
my %combined = (%hash1, %hash2);
my $t1 = new Benchmark;
print "Combining took:",timestr(timediff($t1, $t0)),"\n";
$t0 = new Benchmark;
map { $hash1{$_} = $hash2{$_} } keys %hash2;
my $t1 = new Benchmark;
print "Map took:",timestr(timediff($t1, $t0)),"\n";