Object Teams, or OT/J for short, is a solution for the old Java problem “there is no I in ‘team'”: Most Java code is written as if the whole world was openly hostile. It’s riddled with final, private static, singletons, thousands of lines of code which almost do what you need except for this one line .. that you can’t change without copying the other 999.
Groovy’s solution: AST transformation. A topic for another post.
OT’s solution: create a Java-like programming language which allows you to extend code that isn’t meant to. A great example: Extending Eclipse’s Java compiler.
The Eclipse Java compiler is one of the most complex pieces of code in Eclipse (“5 Mbytes of source spread over 323 classes in 13 packages“). Unlike other compilers, it can compile broken code. The same technology is used to create byte code and error markers in the editor.
Stephan Herrmann wanted to add support for @NonNull and @Nullable. Usually, you’d create a branch, keep that branch in sync with the main branch, etc. Tedious. For every change that someone makes in the main branch, you must update your development branch. Even if the change is completely unrelated. CVS has a very limited concept of “related”. DVCS like Git or Mercurial are better at merging but they also don’t understand enough of Java to give the word “related” a useful meaning. “Same file” is the best you can get.
So instead of the tedious way, he used OT/J to create an OT/Equinox plug-in which patches the JDT compiler byte code. Sounds dangerous? Well, OT/J does all the ugly work. You just say “when this method is called, do this, too.” Sounds a bit like AOP? Yes.
Unlike AOP, it communicates intent more clearly. The code wasn’t designed to be the most compact way to define a “point cut” and then leave it to the reader to understand what this is supposed to mean. It better communicates the intent.
I’m not completely happy with the syntax, though. I don’t have specific points, only a general wariness. Maybe a careful application of Xtext would help.
Related Articles:
- The Next Best Thing – Series in my blog where I dream about the future of software development
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