Add php impls of null object pattern

README.md

@@ -32,7 +32,7 @@ abstract-factory | [DONE](./src/abstract-factory/abstract-factory.md) | [DONE](.
 factory-method | [DONE](./src/factory-method/factory-method.md) | [DONE](./src/factory-method/cpp) | [DONE](./src/factory-method/java) | [DONE](./src/factory-method/python) | [DONE](./src/factory-method/php)
 chain-of-responsibility | [DONE](./src/chain-of-responsibility/chain-of-responsibility.md) | [DONE](./src/chain-of-responsibility/cpp) | [DONE](./src/chain-of-responsibility/java) | [DONE](./src/chain-of-responsibility/python)
 iterator | [DONE](./src/iterator/iterator.md) | [DONE](./src/iterator/cpp) | [TODO] | [DONE](./src/iterator/python) | [DONE](./src/iterator/perl)
-null-object | [DONE](./src/null-object/null-object.md) | [DONE](./src/null-object/cpp) | [TODO] | [DONE](./src/null-object/python)
+null-object | [DONE](./src/null-object/null-object.md) | [DONE](./src/null-object/cpp) | [TODO] | [DONE](./src/null-object/python) | [DONE](./src/null-object/php)
 object-pool | [DONE](./src/object-pool/object-pool.md) | [TODO] | [TODO] | [DONE](./src/object-pool/python)
 private-class-data | [TODO] | [TODO] | [TODO] | [TODO]
 

src/null-object/php/Logger.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * @name Logger interface is a contract for logging something
+ *
+ * Key feature: NullLogger MUST inherit from this interface like any other
+ * Loggers.
+ */
+public interface Logger {
+	/**
+	 * @param string $str
+	 *
+	 * @return mixed
+	 */
+	public function log($str);
+}

src/null-object/php/NullLogger.php

@@ -0,0 +1,38 @@
+<?php
+
+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.
+ * 
+ * Key feature : of course this logger MUST implement the same interface (or
+ * abstract) like the other loggers.
+ */
+
+class NullLogger implements LoggerInterface {
+	/**
+	 * @param string $str
+	 */
+	public function log($str) {
+		// do nothing
+	}
+}

src/null-object/php/PrintLogger.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * PrintLogger is a logger that prints the log entry to standard output
+ */
+class PrintLogger implements Logger {
+	/**
+	 * @param string $str
+	 */
+	public function log($str) {
+		echo $str;
+	}
+}

src/null-object/php/Service.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * Service is a dummy service that uses a logger
+ */
+class Service {
+	/**
+	 * @var Logger Interface
+	 */
+	protected $logger;
+	/**
+	 * we inject the logger in ctor and it is mandatory
+	 *
+	 * @param Logger $log
+	 */
+	public function __construct(Logger $logger) {
+		$this->logger = $logger;
+	}
+
+	/**
+	 * do something
+	 */
+	public function doSomething() {
+		/**
+		 * no more check "if (!is_null($this->logger))..." with the NullObject
+		 */
+		$this->logger->log('We are in ' . __METHOD__);
+		// do actual action
+	}
+}
+
+?>