PHP Enums Library

This library provides enum functionality similar to the implementation found in Java. It differs from existing libraries by offering one-shot enum constructors through static initialization, enum iteration as well as equality support and value, ordinal and binary lookups.

Required PHP version: 5.3

Licensed under the MIT license, see LICENSE for more information.

Introduction

If you want to get started right away, zoom right to 'Getting Started'.

Enumerations can be used to define a fixed set of constants. As this Java-article points out, in most languages people will resort to using integer constants losing useful features in the process.

For example, in your web application you might be using a set of opcodes to communicate with upstream services:

define('OPCODE_VOID', 0);
define('OPCODE_LOGIN', 1);
define('OPCODE_QUERY', 2);
define('OPCODE_LOGOUT', 3);

We may call this an enumeration as it is a set of constants related to each other indicated by their prefix. Consider having a send() method which heavily relies on the defined opcodes. Its usage may look like this:

function send($opcode, $data=null) { }

One would pass in one of the defined constants - ranging from 0 to 3 - and some additional data, and the send() method will do its job:

send(OPCODE_LOGIN, array('name'=>'Pete'));

However, there are a set of disadvantages to this approach:

• No Type-Safety - One could pass in '4' which is not a valid opcode
• No Namespace - Collisions may occur when using global constants
• Uninformative - Debugging $opcode will result in a 'useless' number
• No Behaviour - No behaviour can be attached to the constant
• No Data - No data can be attached to the constant

By using enumerations one can overcome all these disadvantages and in the process benefit from added functionality:

class Opcode extends Enum {

    const VOID = 0;
    const LOGIN = 1;
    const QUERY = 2;
    const LOGOUT = 3;

}

And its basic usage:

function send(Opcode $opcode, $data=null) { }

When '4' is passed in, PHP will throw a type-mismatch exception. The enumeration library magically creates Opcode instances for each specified constant. This will allow our send() method to function correctly:

send(Opcode::LOGIN(), array('name'=>'Harry'));

As for how this works and how to get the most out of the library start with the API example in /examples/api.php

Getting Started

The examples found in the library attempt to visualize real-world situations. Additionally, they are independent and can each be used as a starting point for your own project.

• API: Introduction to the PHP Enums Library
• Binary: Combining enums using masks & flags
• Constructors: Enhancing enums by attaching data and behaviour
• Iteration: Working with a list of defined enums
• Sets: Creating and using unique collections of enums