Template Method Design Pattern in PHP

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In the Template Pattern an abstract class will define a method with an algorithm, and methods which the algorithm will use. The methods the algorithm uses can be either required or optional. The optional method should by default do nothing.

The Template Pattern is unusual in that the Parent class has a lot of control.

In this example, the TemplateAbstract class has the showBookTitleInfo() method, which will call the methods getTitle() and getAuthor(). The method getTitle() must be overridden, while the method getAuthor() is not required.

<?php

abstract class TemplateAbstract {
    //the template method 
    //  sets up a general algorithm for the whole class 
    public final function showBookTitleInfo($book_in) {
        $title = $book_in->getTitle();
        $author = $book_in->getAuthor();
        $processedTitle = $this->processTitle($title);
        $processedAuthor = $this->processAuthor($author);
        if (NULL == $processedAuthor) {
            $processed_info = $processedTitle;
        } else {
            $processed_info = $processedTitle.' by '.$processedAuthor;
        }
        return $processed_info;
    }
    //the primitive operation
    //  this function must be overridded
    abstract function processTitle($title);
    //the hook operation
    //  this function may be overridden, 
    //  but does nothing if it is not
    function processAuthor($author) {
        return NULL;
    } 
}

class TemplateExclaim extends TemplateAbstract {
    function processTitle($title) {
      return Str_replace(' ','!!!',$title); 
    }
    function processAuthor($author) {
      return Str_replace(' ','!!!',$author);
    }
}

class TemplateStars extends TemplateAbstract {
    function processTitle($title) {
        return Str_replace(' ','*',$title); 
    }
}

class Book {
    private $author;
    private $title;
    function __construct($title_in, $author_in) {
        $this->author = $author_in;
        $this->title  = $title_in;
    }
    function getAuthor() {return $this->author;}
    function getTitle() {return $this->title;}
    function getAuthorAndTitle() {
        return $this->getTitle() . ' by ' . $this->getAuthor();
    }
}

  writeln('BEGIN TESTING TEMPLATE PATTERN');
  writeln('');
 
  $book = new Book('PHP for Cats','Larry Truett');
 
  $exclaimTemplate = new TemplateExclaim();  
  $starsTemplate = new TemplateStars();
 
  writeln('test 1 - show exclaim template');
  writeln($exclaimTemplate->showBookTitleInfo($book));
  writeln('');

  writeln('test 2 - show stars template');
  writeln($starsTemplate->showBookTitleInfo($book));
  writeln('');

  writeln('END TESTING TEMPLATE PATTERN');

  function writeln($line_in) {
    echo $line_in."<br/>";
  }

?>
BEGIN TESTING TEMPLATE PATTERN

test 1 - show exclaim template
PHP!!!for!!!Cats by Larry!!!Truett

test 2 - show stars template
PHP*for*Cats

END TESTING TEMPLATE PATTERN

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