add a template method

TemplateMethod/Journey.php

@@ -0,0 +1,76 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\TemplateMethod;
+
+/**
+ * Template Method is a behavioral design pattern.
+ * 
+ * Perhaps you have encoutered it many times already. The idea is to let subclasses
+ * of this abstract template "finish" the behavior of an algorithm.
+ * 
+ * A.k.a the "Hollywood principle" : "" Don't call us, we call you. ""
+ * This class is not called by subclasses but the inverse.
+ * How ? With abstraction of course. 
+ * 
+ * In other words, this is a skeleton of algorithm, well-suited for framework 
+ * libraries. The user has just to implement one method and the superclass do
+ * the job.
+ * 
+ * It is an easy way to decouple concrete classes and reduce copy-paste, 
+ * that's why you'll find it everywhere.
+ */
+abstract class Journey
+{
+
+    /**
+     * This is the public service provided by this class and its subclasses.
+     * Notice it is final to "freeze" the global behavior of algorithm.
+     * If you want to override this contract, make an interface with only takeATrip() 
+     * and subclass it.
+     */
+    public final function takeATrip()
+    {
+        $this->buyAFlight();
+        $this->takePlane();
+        $this->enjoyVacation();
+        $this->buyGift();
+        $this->takePlane();
+    }
+
+    /**
+     * This method must be implemented, this is the key-feature of this pattern
+     */
+    abstract protected function enjoyVacation();
+
+    /**
+     * This method is also part of the algorithm but it is optional.
+     * This is an "adapter" (do not confuse with the Adapter pattern, not related)
+     * You can override it only if you need to.
+     */
+    protected function buyGift()
+    {
+        
+    }
+
+    // this method will be unknown by subclasses (better)    
+    private function buyAFlight()
+    {
+        echo "Buying a flight\n";
+    }
+
+    // sbclasses will get access to this method but cannot override it and 
+    // compromise this algorithm (warning : cause of cyclic depedencies)
+    final protected function takePlane()
+    {
+        echo "Taking the plane\n";
+    }
+
+    // A note regarding the keyword "final" : don't use it when you start coding :
+    // add it after you narrow and know exacly what change and what remain unchanged
+    // in this algorithm. 
+    // [abstract] x [3 access] x [final] = 12 combinations, it can be hard !
+}