Tuesday, July 22, 2008

ActionScript: Literal XML

One feature of ActionScript I really like is the ability to use XML within the language. In ActionScript there's no need to use strings to represent XML, you can use XML inline just as you would any other literal (numbers, strings, etc).

Recently I was working on some dynamic code that needed to update based on an XML response. We were just getting started on the card, so instead of worrying about the service, how it was triggered, etc, we added a button to the interface that called the response parsing method and passed in an XML literal as an argument. The code is similar to what's shown below.


Sure, we had to change the code later and make a real service call, but this quick solution let us keep focusing on the task at hand instead of how to get the XML. In a language like Ruby we could have used a builder or just a string, and given such a small amount of XML it would have been fine. However, the actual XML we were working with was significantly larger than the example and would have been a decent mess of a multiline string or several builder calls. Being able to write XML natively was significantly easier.

The beauty of literal XML is the simplicity. I don't have to represent it in any way other than what it actually is -- XML.

If you aren't a fan of all the angle brackets, that's okay, ActionScript has you covered there also. You can add elements and attributes as you would expect to be able to if you prefer method calls.

var request:XML = <smart_list/>;
request.sort.order = "highest";
request.sort.field = "Average Position";
request.max_results = 10;
request.toXMLString(); // "<smart_list><sort><order>highest</order><field>Average Position</field></sort><max_results>10</max_results></smart_list>"

If you only ever use XML similar to the above syntax, then there may be little value in literal XML, but I don't think you're usage would be limited to the above syntax.

I write tests, a lot of them. I prefer to see the actual XML in my tests, instead of the builder versions of XML. I don't like angle brackets any more than the next programmer, but I strongly prefer testing with expected literals. I find my resulting tests to be more readable and reliable. If you've ever had a test fail because of whitespace issues in your XML, you should know what I mean by reliable.

Literal XML also ensures XML compliance at compile time and encourages IDEs to provide syntax highlighting. Two things that aren't essential, but are definitely nice to have.

ActionScript is the first language I've used with literal XML support, and I'm very happy with the experience. As programmers we spend a lot of time hiding other languages with object relational mappers (orm) and builders, but literal XML is a refreshing step in the other direction. The creators of ActionScript have embraced the fact that XML isn't going anywhere. They built first class support for XML in the language itself instead of hiding the problem with a framework, and that helps me significantly more than any orm or builder ever has.

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