C:\Users\Andy\Documents>perl test.pl
    Length of string: 101000000
    Time taken was  0 wallclock secs ( 0.17 usr  0.03 sys +  0.00 cusr
+  0.00 csys =
     0.20 CPU) seconds

    Time taken was  1 wallclock secs ( 1.13 usr  0.03 sys +  0.00 cusr
+  0.00 csys =
     1.16 CPU) seconds
    C:\Users\Andy\Documents>
[download]

    my $new_string = testing_string($string);

    sub testing_string {
        my $content = $_[0];
        # do some stuff
        $content =~ s/a/b/sg;
        return $content;
    }
[download]

    # do stuff here
    my %test_var;
    $test_var{$string} = $string;
    testing_string();
    $string = $test_var{$string};

    sub testing_string_2 {
        # do some stuff here
        $test_var{$string} =~ s/a/b/sg;  
    }
[download]

Not sure what you mean?

I meant exactly what I wrote: Passing a string to a function doesn't make a copy. Assigning it to a separate variable does. So

sub f {
    print $_[0];
}
[download]

avoids the copy, whereas

sub f {
    my $x = $_[0]; # copy created here
    print $x;
}
[download]

creates one.

Since it's quite ugly to use $_[NUMBER] all the time, I suggested references instead.

Perl 6 - second systems done right

Aaaah ok - missed that reply =) That would explain why testing1() is considerably quicker than testing2() in the below:



sub testing1 {
  print "At testing1 \n";
  $_[0] =~ s/foo/test/g;
}

sub testing2 {
  print "At testing2 \n";
  my $string = $_[0];
  $string =~ s/foo/test/g;
  return $string;
}
[download]

Thanks!

Andy

    my $new_string = testing_string($string); 

    sub testing_string {
        my $content = $_[0]; #string copy, expensive
        # do some stuff
        $content =~ s/a/b/sg;
        return $content; #string copy, expensive
    }
[download]

   # do stuff here
    my %test_var;
    $test_var{$string} = $string; # double!! string copy and hash 
                     # sum calculation, expensive. And why   
                     # this senseless copying into a hash? a scalar 
                     # variable (i.e $string) is global too
    testing_string();
    $string = $test_var{$string}; # string copy and hash sum calculati
+on of $string

    sub testing_string_2 {
        # do some stuff here
        $test_var{$string} =~ s/a/b/sg;  
    }
[download]

What you could do is this:

   testing_string(\$string); #send a reference to $string instead of $
+string

    sub testing_string {
        my $contentref = $_[0];
        # do some stuff
        $$contentref =~ s/a/b/sg;
   }
[download]

But are you sure you have problems with the speed of your script? Did you profile your script to see where it is slow? You might google for "premature optimizations", this is the most common mistake programmers make. And as you can see, often they even make it more expensive because they don't know enough about the underlying mechanism.

Simply copying strings is a very fast operation on modern CPUs because they can use special instructions (maybe even DMA transfers) for it. You might only save micro- or milliseconds if this operation is not done thousand or million times in your script