Perl Module Basics

uses the arrow operator,  >. The left hand side of the arrow operator must be either 

a package name (such as IO::File) or an object (such as $filehandle). The right 

hand side is the name of a subroutine to call.

Methods automatically receives as an extra initial parameter the variable on 

the left hand side of the arrow operator. You can imagine that the call to new() is 

translated into the following:

my $filehandle = IO::File::new("IO::File", "> file.txt");

But you shouldn't write it that way using method call syntax enables Perl's inher 

itance to work. I'll describe inheritance in more detail later.

Perl offers another method call syntax known as indirect object syntax. Here's 

the code from the example rewritten to use indirect object method calls:

my $filehandle = new IO::File ">file.txt";

print $filehandle "This line goes into file.txt\n";

close $filehandle;

In this style, the method name comes first followed by either a package name or an 

object. Both calling styles result in the same method invocation the extra initial 

argument is supplied to the method subroutine in both cases. Choosing which one 

to use is largely a matter of preference, although many Perl programmers prefer 

the arrow notation since it is less visually ambiguous. Furthermore, Perl itself 

occasionally has trouble parsing indirect object syntax. For these reasons, I'll be 

using arrow notation in my examples from this point forward.

CAUTION C++ programmers take note there is nothing special about 

methods named new(). It is only by convention that constructors are 

often named new().

A method that is called using a package name is a class method. A method 

called with an object is an object method. Class methods are used to provide services 

that are not specific to any one object; object construction is the most common 

example but I'll explore others in the next sections.

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