How to model a templating class

[geek5]

I am writing a basic templating class for my own project. The basic usage is this:\[code\]$template = new Template('template_file.php');$template->assignVariable('pageTitle', 'Home page');$template->render();\[/code\]Contents of 'template_file.php':\[code\]<?php print $pageTitle; ?>\[/code\]This is what template class does step by step:[*]Stores variables in a private array when assignVariable method is called[*]When render method is called, extracts stored variables, includes template file in a \[code\]ob_start()\[/code\] and \[code\]ob_end_clean()\[/code\] block. Stores output in a variable with \[code\]ob_get_contents()\[/code\] and then prints stored output.I know this is a very simple templating class but works as expected. The question is should I delegate the including the template file to another class? I had this question when I was writing the unit tests for this class. I thought that file system interaction should be encapsulated. What do you think? If you think that it should not, how can I mock including a file in my tests?Maybe I just pass the contents of the template file to the class like this:\[code\]$templateContent = file_get_contents('template_file.php');$template = new Template($templateContent);...\[/code\]Edit: I decided to encapsulate the input process of template class for the sake of writing better unit tests and encapsulation. But as johannes pointed out, I needed to use \[code\]eval()\[/code\] for that purpose which seemed not right. Johannes pointed me to the direction of stream wrappers for mocking the including in unit tests. But that inspired a new idea on me. Here is what I am going to do; I will continue to use \[code\]include()\[/code\] in my template class but this time with stream wrappers. I will pass protocol handler to my template class while initializing it. This way I can create my own stream wrappers for fetching template data from database or using a local variable. Here are the examples:\[code\]$template = new Template('file://template_file.php');stream_wrapper_register('database', 'My_Database_Stream');$template = new Template('database://templates/3'); // templates table, row id 3stream_wrapper_register('var', 'My_Var_Stream');$myTemplate = '<?php print "Hello world!"; ?>';$template = new Template('var://myTemplate');\[/code\]I have already implement custom stream wrapper for local variables. Here it is:\[code\]class My_Var{ protected $position; protected $variable; function stream_open($path, $mode, $options, &$openedPath) { $url = parse_url($path); global $$url['host']; $this->variable = $$url['host']; $this->position = 0; return true; } public function stream_read($count) { $ret = substr($this->variable, $this->position, $count); $this->position = strlen($ret); return $ret; } public function stream_eof() { return $this->position >= strlen($this->variable); }}stream_wrapper_register('var', 'My_Var');$myvar = '<?php print "mert"; ?>';include 'var://myvar';exit;\[/code\]