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PHP Template Engines?
kubed asks: "I've recently learned how to use PHP template engines to separate business logic from presentation. Some argue that template engines make applications easier to maintain and make for cleaner code. Others argue that template engines introduce unnecessary overhead and require too much additional processing power. Do the readers of Slashdot think that it is important to use templates or are they just an extra unnecessary layer? There are dozens of PHP template engines to choose from including Smarty, phplib, and bTemplate. Which template engines do you have experience with and which ones have the best performance?"
There are really two things to consider when using template languages like PHP and ColdFusion:
1) Is the rapid development style worth the processing overhead and system-independence?
2) Are you prepared to take the extra time to make the code clean after said rapid development?
Granted, any language can be misused to create horrible code, but with rapid development with template languages, you have to be careful not to let the ease and simplicity of the language lull you into poor programming. However, you do not need to use extra "stuff" to accomplish this specifically, if you are careful to code your data access modules separate from the presentation logic in the first place, which is just good programming style in general.
I am currently just two weeks away from going live with a large web application written in PHP using Smarty. I can't speak to performance, as it is a complex application with a low number of clients, but for my needs it has been very acceptable. As far as the interface and syntax, I am in love with Smarty. I had become disenchanted with PHP due to the spaghetti code when you don't use such an engine. Smarty .. mmm, it has brought me back. In fact, I'm writing a templating engine for Ruby based on the Smarty syntax.
Smarty -- highly recommended!
I have a template engine based on standards. It's called XSLT, and it's built into the most recent PHP versions. Especially nice is the 5.x branch, since it has been completely rebuilt for speed and compatibility to libxml2. I have a site full of XML, and I transform it with a central XSL template file into the displayed content. It's a shallow learning curve, and I can change the entire site's layout by a few XSL tweaks. For me, it is the perfect solution.
Heute die Welt, morgen das Sonnensystem!
Ok, so I'm a little biased having written my my own template engine. However, they have their plusses and minusses.
On the positive side, it really helps separate code from display, which makes everything look neater -- as in clean, not as in "gee whiz". HTML is easier to read and it's easier to abstract everything. I'm sure you know the arguments for it already. If you need to change something, all you do is find the template and you can see everything in one clear shot, instead of digging through mountains of PHP logic.
Additionally, if you use a good template engine, it will make your pages load faster by using a caching system. Basically, if your page doesn't change very often, it will save a static copy of all of your PHP logic and return that to the browser instead of making the database calls and other operations that eat up processing speed. I did notice a difference when I wrote my site.
However! There are some important things to remember. Unless you cache your site, it will probably not be any faster. Smarty is, in my opinion, bloated and slow. It tries to do too much and takes forever to load and use. (By forever, I mean like 0.1 seconds to load a page created by Smarty versus 0.005 seconds to load the equivalent page from pure PHP.)
Moreover, websites made with templates are summarily locked into that template engine and new developers will have difficulty figuring out what the heck you did without a good bit of explanation.
One more point to consider is the fact that when using template engines, usually you're limited in the tricks you can pull on your website. Template engines seriously restrict your ability to do cool things with PHP in the display process.
Finally, template engines introduce new flaws into your website. Sometimes those flaws are really bad and affect the performance of your site and then the developers are sometimes difficult to work with and then you have this piece of code that you didn't write that you have to work around.
Those are just things to consider.
I write php and for any relevantly grouped output, I surround it in html div tags. I use a lot of div tags. E.g., to deal with a list of links with descriptions, the entire list is enclosed in a div, each link plus it's description has it's own div, each link has it's own div, and each description has it's own div.
I keep a list of the classes/ids of the divs. I heavily organize the code so that every element can easily be referred to by a class or id according to a heavily commented list of selectors.
The PHP file is all structure/programming logic. I put all content in some sort of database.
Then I write cascading style sheets. You'd be amazed at how many different ways you can make the page look. And not just different colors/font sizes; you can make a sidebar float left or right, or be across the top; you can make links' subsections unfold, or stay invisible until you're in that section; in short, you can make the page be layed-out however you want.
(A few caveats: I've found, in making the css cross-browser compatible, that sometimes you need to do a few work-arounds that pollute the structured PHP document, things like: make a extra div around a div; maybe use a conditional statement to show an INPUT or a BUTTON tag. But you usually need to pollute your non-css HTML anyway if you want to do some sort of tricky design that is cross-browser compatibile and that degrades gracefully.)
For me, a separate PHP template engine means that the template itself will be polluted: you'll have HTML that's trying to do design, instead of just describing the page's structure. And of course, the template page will need some programming logic like loops and conditionals.
Better for your designers learn css than make them deal with some half-assed half-HTML, half-PHP template.
1) With PHP templates
--
* programming logic in php files
* content in a database
* structure/design in template
2) With no templates but using css
--
* programming logic & document structure in PHP files
* content in database
* design in css
Two is cleaner, no?
Check out the SitePoint forums for Advanced PHP. The pro's and con's of template engines have been discussed over there in length and it is just a great resource for advanced PHP topics. SitePoint Forums.
Also, take a look at Harry Fuecks website PhpPatterns. He also has detailed information about PHP templating and the theory behind the code.