Re: Anonymous Data Structures

I had to look up anonymous data structures to figure out what you were referring to and it appears that they are just talking about references. THAT I can help you with.

Normally there are two ways of working with a variable, making a copy of it, or using a reference to it. A simplified example would be a sign-in sheet for a writing class. You want everyone to write their name on the sheet so you have to get information from everyone. There are two ways of doing this,

Make a copy of it.
1. make a copy of the sign-in sheet.
2. have the student sign the sheet new copy.
3. Get the copy back from the student.
4. Throw away the old sign-in sheet and go back to step 1. Repeat until finished
Use a reference

Take a sign-in sheet.
Have the student sign their new on the sign-in sheet
Repeat until finished.

The first way sounds stupid, but you will be surprised how often it occurs, especially with beginners. Here is code to show how it works.

#!/usr/bin/perl

use strict;
use warnings;

# Make a copy of a variable

my $counter = 0;
print "Copying and replacing the variable\n";
for (1..10) {
    $counter = increment_number( $counter );
    print "Count is $counter\n";
}

$counter = 0;
print "Passing a reference to the variable\n";
for (1..10) {
    increment_number( \$counter );
    print "Count is $counter\n";
}

sub increment_number {
    my $number = shift;

    if (ref $number eq 'SCALAR') {
        $$number++;
        return;
    }
    return ++$number;
}
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Re^2: Anonymous Data Structures by lwicks (Friar) on Jun 01, 2007 at 15:56 UTC
Hi Herkum, So colour me a noob, but what you are saying is in your first example we are chewing up memory creating a copy of $counter. Whereas in the second example we are pointing to the original. The implication being that example two is more efficient/faster/leet? Is that right. Lance Kia Kaha, Kia Toa, Kia Manawanui! Be Strong, Be Brave, Be perservering!	[reply]
Re^3: Anonymous Data Structures by Herkum (Parson) on Jun 01, 2007 at 21:12 UTC
your first example we are chewing up memory creating a copy of $counter Correct. in the second example we are pointing to the original. The implication being that example two is more efficient/faster/leet? Is that right. Correct as well. The example I used does not really offer any performance benefits because it is too small. Lets supposed you have a million element array. In the first example you would, create 2 copies of that million element array in your program(So it takes more memory). You would also be passing million values to and from the function(so it would be slower). If you use a reference you have one copy of that array. You only passing a single value to the function. This can be provide enormous performances benefits when working with a large amount of data. There are times you want to make a copy because you don't want to change the original data. But if you are modifying the original values you should use references.	[reply]