#! /usr/local/bin/perl -l

package P;

sub new {
    my $class = shift;
    my $mod   = shift;
    eval "use $mod ()";
    my $self = {};
    if ($@) {
        $self->{_time_func} = sub { time };
    }
    else {
        $self->{_time_func} = sub { Time::HiRes::time() };
    }
    return bless $self, 'P'
}

package main;

my $p = P->new( shift || 'Time::HiRes' );

print $p->{_time_func}->();
sleep 2;
print $p->{_time_func}->();