Structural patterns

In this section, we will take a look at a structural pattern: the decorator pattern.

The decorator pattern

The decorator pattern is a simple one. It allows us to add new behavior to object instances without affecting other instances of the same class. It basically acts as a decorating wrapper around our object. We can imagine a simple use case with a Logger class instance, where we have a simple logger class that we would like to occasionally decorate, or wrap into a more specific error, warning, and notice level logger.

The following example demonstrates a possible decorator pattern implementation:

<?php

interface LoggerInterface
{
    public function log($message);
}

class Logger implements LoggerInterface
{
    public function log($message)
    {
        file_put_contents('app.log', $message . PHP_EOL, FILE_APPEND);
    }
}

abstract class LoggerDecorator implements LoggerInterface
{
    protected $logger;

    public function __construct(Logger $logger)
    {
 ...