How can I use Eclipse's new Xtend language in my Android project?

Question

I'd like to write Java classes in the Xtend language (simply because its way more terse), and have it compile back down into Java classes of which I can use in my Java project. Just like coffeescript. How can I do this?

I tried creating an Xtend file just as I would do with a new class, however I get this error:

Mandatory library bundle 'org.eclipse.xtext.xbase.lib' not found on the classpath.

This disables intellisense (autocompletion). Also, even if I do get that working, how can I have it compile to a Java class?

Answer 1

In Xtend inner classes are dereferenced using a dollar sign ('$') and static members are accessed using a double colon ('::').

The HelloAndroid activity code would look like this:

class XtendActivity extends Activity {

    override void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R$layout::main);
    }
}

Answer 2

Having tried the same thing, I can confirm that enabling the Xtend Nature and adding the three Xtend libraries (mentioned earlier, 'org.eclipse.xtext.xtend2.lib', 'org.eclipse.xtext.xbase.lib' and 'com.google.inject') to the project's libraries makes the Xtend code compile, at least. However, I am also having trouble with the R class.

On closer inspection, it looks like the problem with the R class is not with it being located in a different directory. Copying the file to the main source dir with a different name doesn't change anything. Rather, it looks like the problem is with the R class being a static final class, containing several static final subclasses. If I create a simple plain-Java wrapper class that wraps a reference to R.layout.main (for example) inside a normal method, and call that from my Xtend code, then it does accept it and happily compiles.

After that, the next issue I came across was the Android compiler complaining about duplicate about.html and plugin.properties files in 'org.eclipse.xtext.xtend2.lib', 'org.eclipse.xtext.xbase.lib' and 'com.google.inject'. That is relatively easy to fix, by removing those files from two of the three .jar files. I'm not sure if it breaks anything later on, but now at least I have a working snippet of Xtend code running on the Android emulator.