Introduction

OOP. Object oriented programming. The reason some say Ruby is better than Perl. The reason some say Perl is better than Ruby. Most job ads require applicants have knowledge of it. It’s simultaneously fad and revolution, silly gimmick and sanity savior.

OOP is often feared. “How much extra programming will I have to do?” “How difficult is it to pick up?” “Won’t the internals be hopelessly obfuscated?” “It’s slower than an equivalent procedural script, isn’t it?”

The task

We are going to develop an object oriented module. It will...

1. provide methods (OO subroutines) to easily print colored HTML text
2. support any named color (eg, “blue” or “green”) recognized by browsers, so these will work:
   1. print $color->magenta("Wow, what a color!");
   2. print $color->vermilion("I can't believe this works.");
3. also support any hexadecimal colors (e.g.: “#DF303C”) with a method for each, so these will work:
   1. print $color->DF303C("Colored text here");
   2. print $color->336699("This is a websafe color");
4. also support any user defined colors with a method for each, so something like these will work:
   1. print $color->virgin_green("Underage ETs!");
   2. print $color->HausBraun("Not to be confused with Eva.");
   3. print $color->pantone_process_blue("Yawn...!");
5. and because of 2-4, the modules will contain an unlimited number of methods

Sound difficult? Like most everything in Perl it’s not, once you know how it can be done. We can do this in about 10 lines of code. No lie. Take a look.

package OOPminiscule;
#=====================================================================
sub new { return bless \$empty_scalar, shift }
#=====================================================================
sub AUTOLOAD {
    no warnings;
    my ( $color ) = $AUTOLOAD =~ /^.+::(\w+)$/;
    $color = $color =~ /^[A-F0-9]{6}$/ ? "#$color" : $color;
    *{$AUTOLOAD} = sub {qq|<span style="color:$color">| . 
                            join($",@_[1..$#_]) .
                                "</span>\n" };
    &{$AUTOLOAD};
}
1;

my $cm = OOPminiscule->new();  # "cm" for color maker

print 
    $cm->red("HEY! That's incorrect."),
    "<br />\n",
    $cm->D71986("Wha! That's not a websafe color!"), 
    "<br />\n",
    $cm->blue("* please see the instructions");

HEY! that's incorrect.
Wha! That's not a websafe color!
* please see the instructions

…what?! First you should know, in case you don’t already, the code won’t work for some cases in Task item 3 (3.b. would break the module, for example) and won’t work at all for case 4 yet. Let’s come back to this ungodly idiom in minute.

Wait, what’s OOP again?

In the perldoc perltoot Perl demi-god, Tom Christiansen, describes object oriented programming this way (quote is abbreviated):

An object is nothing but a way of tucking away complex behaviors into a neat little easy-to-use bundle. This is [called] abstraction… …The heart of objects is the class, a private namespace full of data and functions. Objects “live” in a class, meaning that they belong to some package.

It’s simple once you get it. An object is just a reference, a pointer, to some data which is aware of its own namespace (methods/subroutines that belong to it). It can contain any number or style of datum and have easy access to functions from its class or its relatives (parents, super classes, etc).

Page 2, OOP