From ceeab58eb9df78820a12588f1bef635693bc3cb9 Mon Sep 17 00:00:00 2001
From: Trismegiste <florent.g@allopneus.com>
Date: Mon, 13 May 2013 21:49:33 +0200
Subject: [PATCH] add a simple example with a null logger

---
 NullObject/LoggerInterface.php | 16 ++++++++++++++
 NullObject/NullLogger.php      | 38 ++++++++++++++++++++++++++++++++++
 NullObject/PrintLogger.php     | 20 ++++++++++++++++++
 NullObject/Service.php         | 30 +++++++++++++++++++++++++++
 4 files changed, 104 insertions(+)
 create mode 100644 NullObject/LoggerInterface.php
 create mode 100644 NullObject/NullLogger.php
 create mode 100644 NullObject/PrintLogger.php
 create mode 100644 NullObject/Service.php

diff --git a/NullObject/LoggerInterface.php b/NullObject/LoggerInterface.php
new file mode 100644
index 0000000..2c6ed97
--- /dev/null
+++ b/NullObject/LoggerInterface.php
@@ -0,0 +1,16 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * LoggerInterface is a contract for logging something
+ */
+interface LoggerInterface
+{
+
+    public function log($str);
+}
\ No newline at end of file
diff --git a/NullObject/NullLogger.php b/NullObject/NullLogger.php
new file mode 100644
index 0000000..58a67e0
--- /dev/null
+++ b/NullObject/NullLogger.php
@@ -0,0 +1,38 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * NullOutput is a example of NullObject pattern. It is not formely a Design
+ * Pattern by the GoF but it's a schema which appears frequently enough to
+ * be a pattern. Futhermore it is a really good pattern in my opinion :
+ * - the code in the client is simple
+ * - it reduces the chance of null pointer exception
+ * - less "if" => less test cases
+ * 
+ * The purpose : every time you have a method which returns an object or null,
+ * you should return an object or a "NullObject". With NullObject, you don't need
+ * statement like "if (!is_null($obj)) { $obj->callSomething(); }" anymore.
+ *  
+ * In this case, this a logger which does nothing. Other examples :
+ * - null logger of symfony profiler
+ * - null output in symfony/console 
+ * - null handler in a Chain of Responsiblities pattern
+ * - null command in a Command pattern
+ * 
+ * Performance concerns : ok there is a call for nothing but we spare an "if is_null"
+ * I didn't run a benchmark but I think it's equivalent.
+ */
+class NullLogger implements LoggerInterface
+{
+
+    public function log($str)
+    {
+        
+    }
+
+}
\ No newline at end of file
diff --git a/NullObject/PrintLogger.php b/NullObject/PrintLogger.php
new file mode 100644
index 0000000..4640ca4
--- /dev/null
+++ b/NullObject/PrintLogger.php
@@ -0,0 +1,20 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * PrintLogger is a logger that prints the log entry to standard output
+ */
+class PrintLogger implements LoggerInterface
+{
+
+    public function log($str)
+    {
+        echo $str;
+    }
+
+}
\ No newline at end of file
diff --git a/NullObject/Service.php b/NullObject/Service.php
new file mode 100644
index 0000000..f1eaf33
--- /dev/null
+++ b/NullObject/Service.php
@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * Service is dummy service that uses a logger
+ */
+class Service
+{
+
+    protected $logger;
+
+    // we inject the logger in ctor and it is mandatory
+    public function __construct(LoggerInterface $log)
+    {
+        $this->logger = $log;
+    }
+
+    public function doSomething()
+    {
+        // no more check "if (!is_null($this->logger))..." with the NullObject pattern
+        $this->logger->log('We are in ' . __METHOD__);
+        // something to do...
+    }
+
+}
\ No newline at end of file