ColdFusion Custom Tags And High Coupling

As I see it, there are two main types of custom tags:

One is library tags which are application neutral and do some task. For example, I have a 'tovar' tag that acts like CFSAVECONTENT but with the ability to append or override, as well as accept a VALUE attribute. I use it all over the place. Same interface, same functionality, same behaviour.

The other is application tags, which are tightly coupled to the application and serve to hold part of the application logic in a reusable component (other than a CFC). I usually use these for layout things, such as a 'link' tag which accepts an objectId to link to and translates it into an appropriate link (using some application-specific logic to compute the URL). I use a 'link' tag in multiple applications, but while the interfaces are all the same, each one's implementation is totally different, and depend heavily on environment (specially application-level singletons). Same interface, same functionality, application-specific behaviour.

There's definitely a place for both types of tags.

Great question and if you don't mind me asking what framework were you looking at from CFPetMarket that had that example?? I'm going to guess the SAM Methodology as I work with Simon Horwith and know his unquestionable passion for custom tags. ...And also for his heavy use of single quotes!! I'm pretty sure it has to be that one. :)

I personally use custom tags only for output. For example, my layout template, displaying a query with an XHTML table, pagination, etc. Many believe components shouldn't be used for output and I think its best to stick to that belief although it can depend on what you are trying to do. I do my best to encapsulate my components and I do the same for my custom tags. I definitely suggest both although don't beat yourself up trying to decide. Do what you best suits you.

You're right in thinking that components should be black boxes with wires going in and one wire going out. The single return value can be a structure and thus contain many results.

I think that since components are a relatively new phenom, some people are still using custom tags.

I use a custom tag to do a SELECT and then cfset FORM.variables that are in the Columnlist. But that's it's purpose.

I think the idea is: "If I were to post this to cfLib, is it written correctly?"
For expediency, most people don't write for cfLib support.
In fact, most people don't spend a lot of time looking through a lot of code for inspiration; so treasure these days where you see things through a student's perspective!

"In fact, most people don't spend a lot of time looking through a lot of code for inspiration; so treasure these days where you see things through a student's perspective!"

I totally disagree! I'm constantly digging through code for inspiration! I've really begun to love using Ben's programmatic configuration code and have always looked to others to see how it is they solve their problems to see what their approach was. It's probably more for implementation than inspiration but nonetheless you'd be amazed at how many developers still go digging through code.

I think a lot of the coupling you see in custom tags is because plenty of code using such tags is a little older and while OO devotees (who are particularly focused on minimizing unnecessary coupling) use custom tags, lots of NON OO programmers also use custom tags so it seems likely that you'd see more coupling in custom tags.

I think on the whole it is a bad thing to have a custom tag knowledgeable about its environment as it is not only less reusable, but also it makes the code less maintainable unless you have great documentation about the dependencies which is shared with all of the developers. It also makes unit testing of the tags harder.