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Perl object-oriented programming

A brief introduction to the module

The module is the Perl package (pachage). Objects in Perl are based on references to data items in the package. (for references, see Chapter x references).

See http://www.metronet.com 's perlmod and perlobj for details.

When object-oriented programming in other languages, first declare a class and then create objects (instances) of that class. All objects of a particular class behave in the same way, determined by class methods. You can create a class by defining a new class or inheriting from an existing class. People who are already familiar with object-oriented programming can encounter many familiar terms here. Perl has always been an object-oriented language, and in Perl5, the syntax has changed slightly to standardize the use of objects.

The following three definitions are critical to understanding how objects, classes, and methods work in Perl.

. Class is a Perl package that contains classes that provide object methods.

. The method is a Perl subroutine and the class name is its * parameters.

. Object is a reference to a data item in a class.

II. Classes in Perl object-oriented programming

Again, a Perl class is just a package. When you see a reference to "class" in the Perl document, just think of it as a "package". The syntax of Perl5 can create classes, and if you are already familiar with Clippers, you have mastered most of the syntax. Unlike Perl4, the concept is to use a double colon (::) to identify base classes and inherited classes (subclasses).

An important feature of object-oriented is inheritance. The inheritance feature in Perl is not exactly the same as other object-oriented languages, it only inherits methods, you must use your own mechanism to achieve data inheritance.

Because each class is a package, it has its own namespace and its own associative array of symbolic names (see Chapter x associative array for details), so each class can use its own independent set of symbolic names. In conjunction with package references, you can use the single quotation mark (') operator to locate variables in a class, such as: $class'$member. In Perl5, you can use double colons instead of single quotation marks to get references, such as: $class'$member is the same as $class::$member.

Third, Perl object-oriented programming to create classes

This section describes the necessary steps to create a new class. The following example is to create a simple class called Cocoa, whose function is to output the necessary part of the source code for a simple Java application. Rest assured, this example does not require you to have knowledge of Java, but it does not make you an Java expert, and its purpose is to talk about the concept of creating classes.

First, create a package file named Cocoa.pm (the extension pm is the default extension of the package, meaning PerlModule). A module is a package, and a package is a class. Add the line "1;" before doing anything else, and when you add other lines, remember to keep "1;" as a line. This is a necessary condition for the Perl package, otherwise the package will not be processed by Perl. The following is the basic structure of the file.

PackageCocoa

# # Put "require" statementsinforallrequired,importedpackages

# #

# Justaddcodehere

# 1 lead terminatethepackagewiththerequired1

Next, we add a method to the package to make it a class. The * method to be added is new (), which must be called when the object is created, and the new () method is the constructor of the object.

Fourth, the constructor

The constructor is a subroutine of a class that returns a reference related to the class name. Combining a class name with a reference is called a "blessing" object, because the function that establishes the union is called bless (), and its syntax is:

BlessYeReference [, classname]

YeReference is a reference to the "blessed" object, and classname is optional, specifying the package name of the object's get method, whose default value is the current package name.

In Perl object-oriented programming, the way to create a build function is to return a reference to the internal structure that has been combined with the class, such as:

Subnew {

My$this= {}; # Createananonymoushash,and#selfpointstoit.

Bless$this;#ConnectthehashtothepackageCocoa.

Return$this;#Returnthereferencetothehash.

}

{} create a reference to a hash table (that is, an associative array) without key / value pairs, and the return value is assigned to the local variable $this. The function bless () fetches the reference and tells the object that it refers to Cocoa,*** and returns the reference. The return value of the function now points to the anonymous hash table.

After returning from the new () function, the $this reference is destroyed, but the calling function saves the reference to the hash table, so the number of references to the hash table will not be zero, causing Perl to keep the hash table in memory. You can call to create an object as follows:

$cup=newCocoa

1#!/usr/bin/perl

2push (@ INC, "pwd")

3useCocoa

4$ cup=newCocoa

The * line indicates the location of the Perl interpreter. In the second line, add the current directory to the path lookup list @ INC for use when looking for packages. You can also create your modules in different directories and indicate the absolute path. For example, if you create a package in / home/test/scripts/

The second line should be as follows:

Push (@ INC, "/ home/test/scripts")

In the third line, include the package Cocoa.pm to get the functionality needed in the script. The use statement tells Perl to find the file Cocoa.pm in the @ INC path and include it in the parsed copy of the source file. Use statements are required to use classes. The fourth line calls the new function to create an object, which is the beauty of Perl, its confusion, and its power. There are several ways to create an object, and you can write:

$cup=cocoa- > new ()

If you are a C programmer, you can use double colons to force the new () function in the Cocoa package, such as:

$cup=Cocoa::new ()

You can add more code to Perl object-oriented programming constructors, such as Cocoa.pm, where you can output a simple declaration when each object is created, and you can use the constructor to initialize variables or set arrays or pointers.

Note:

1. Be sure to initialize variables in the constructor

2. Be sure to use the my function to create variables in the method

3. Never use local in a method unless you really want to pass variables to other subroutines

4. Never use global variables in the class module.

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