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