use Data::Dumper;
use Benchmark qw(timethese);
use strict;
use warnings;

timethese(1000000, {
        'loop' => \&s1,
        'non-loop' => \&s2
    });

sub s1 {
	my %hash = (a => 3, b=> 4, c=>1 ,d=>7); 
	my @sels = qw(b c); 
	delete $hash{$_} foreach (@sels);
}

sub s2 {
	my %hash = (a => 3, b=> 4, c=>1 ,d=>7); 
	my @sels = qw(b c); 
	delete @hash{@sels};
}