Creating a templating engine

Radon3k

I'm looking to create a template engine but not really sure how to go about doing this. I created a pseudo-template engine and it works, but only to a point. Basically I'm keeping the templates in a database and doing a SELECT statement to call them and then putting them into an array and assigning them from there into variables. However if someone wanted to move something around they couldn't do it because it's hard coded into the code, which kind of defeats the purpose unless they're only looking to change the colors. What are some ways that I could go about creating a template engine? Please note that I'm not looking to use anything like Smarty since I want to do this mostly for fun and as a learning experience. I've seen some template engines that use the eval() function though I'm not sure how that fits into the whold grand scheme of things. I guess what I'm looking for is a nudge in the right direction, how the code should work conceptually. I'm not looking for anybody to write the code for me as that would take the fun out of it, just a push in the right direction. Thanks.

AstroTeg

I've built a really simple template engine that fits my needs. I haven't looked at Smarty so I'm not sure what bells and whistles I left out of mine.

Some of the things I thought about when working on mine was what did I need my template engine to do? How did I want to edit my templates? How was I going to store my templates? Because of how I stored them, how was I going to retrieve them? Did I want to embed templates within other templates? If so, how? How do you want to handle the classic table row problem? (you have a table with a ton of rows of data, how do you define a template to show all the rows of data even though the row count will change?) Will you be mixing PHP with HTML in your templates?

These are all things to think about.

I opted to store my templates as html files in a template directory. In the templates I have template tags or variables. These you can insert other templates where these tags/variables are at which has really made it easy to work with. I use regular expressions to find the tags and replace them with my variables. From there, you're basically done and you can send the finished template to the browser.

You mentioned the use of eval(). I don't know if you intend to mix PHP with your templates. If you do, you need to think about the security consequences of doing that. Plus how will you handle errors and bugs? With the template system I went with, I opted to keep only HTML in the templates. This forces me to keep the PHP code seperate from the HTML which has resulted in some really modular PHP files (copy the php file to a new site and just rename or edit the template to fit the new site's look/feel).

These are just ideas and some stuff I bumped into when working on my template engine. You'll probably have different ideas on features you need and want and this is what will drive your engine.

kpzani

I made something similar - but for a specific site not a general website more a dbase front end.

I went down the oop route. Creating classes for everything from menubars, iconbars, tables then pages
so i could go something like

$mypage = new page($title);
page->setColourScheme("Blue");
page->addContent($bightmlblock);
page->render();

I think this method is pretty cool.

generally people create html templates and put special chars in there like %PAGETITLE% then use a reg exp in a function to replace that when you set it.

its also possible to use tags to dictate repetition and so forth.

Theres some good stuff about this in a book called Secure PHP Development published by Wiley.

rehfeld

personally i think people use regex for templates way more often than they need to. sometimes they are definaely warranted, but i see most people using them when either a simple str_replace would work, or when an include would be more suitable.

i also dont see why people want to keep php code out of templates so religiously. the only argument ive really heard is they dont want thier designers messing things up. but if they touch your custom "tag" your template is gonna fail anyway just like if they touched your php code.....

this is essentailly how i do it. its a basic striaghtforward approach that doesnt try to reinvent the wheel. of course this example is extremely basic, implementation exercise left to the reader.


<?php

// index.php or main page etc....

$header = set_include_header($header_args); 
$nav = set_include_nav($nav_args); 
$body = set_include_body($body_args); 

$template = set_template($template_args);

include($template);


?>


// template.php

<html>
<body>
<h1><?php include($header); ?></h1>
<div><?php include($nav); ?></div>
<?php include($body); ?>
</body
</html>

now of course you dont need to include() everything, you could just as easily have set_include_header() be called generate_header() or whatever and then just echo the result as a string.

and you can have a set_css() set_footer() and so on to your hearts desire.

the concept is really just a set of arguments which cascade thier arguments into other sets of arguments.

kpzani

I agree about the regexp comment most of the time a string replace will do. but if have a template structure like

Then regexps will provide much more power with the replacing than standard string replace functions. But it makes the PHP almost unreadable to anyone who isn't up on reg expressions.

The main reason for separating the php from html is if you are making a site / project for a customer. then they can mess about with the pages as muich as they like coz it works verymuch like a mail merge doc.

Generally the stuff I produce has as much php in the html pages as outside. although i do use a lot of requires / includes to get the basic structure and functions / variable / conf files to control a lot of the standard stuff.

I have also been experimenting with php generating css pages. Generally my stylesheets only use three or four colours and 1 font at a few sizes so its quite neat to have the php generate the final style sheet from a few simple base vars - making a h3 2 px's bigger than a p and so on.

Shrike

An interesting read.

I used Smarty in a recent project and came to the same conclusion as Mr Fuecks - the big name templating engines are basically just a wrapper to PHP, and just as complicated!

The best thing I have found from using Smarty is the ability to only expose certain data to the template. Thus when developing templates, the developer is not tempted to start writing business logic into the template itself. This is the way it should be in multi-tiered applications (the template should not be able to query a database). However this can be achieved with general code abstraction (and data hiding in PHP 5). The other neat thing which Smarty does is template caching, but to be honest that's only really there because without caching things can run too slow.

Templating engines are however a godsend in compiled languages, where you don't need to recompile to see if a minor display change worked. As far as PHP is concerned though it's really a bust.