How to tersely define Guice bindings of parametrised classes using Xtend?

Question

The following Java code sets up a Guice binding. It uses an anonymous subclass of AbstractModule that provides an implementation of configure to set the bindings, and anonymous subclasses of TypeLiteral to create a binding of Map to HashMap for specific type parameters (as described here).

injector = Guice.createInjector(new AbstractModule() {
    @Override protected void configure() {
        bind(new TypeLiteral<Map<String, Event>>() {})
            .to(new TypeLiteral<HashMap<String, Event>>() {});
    }
});

How could I write this in Xtend?

As far as I can see, Xtend doesn't support implementing anonymous classes or nested classes (they aren't mentioned in the doc and I haven't been able to guess a working syntax). So I would have to define my AbstractModule and each of my TypeLiteral implementations in separate Xtend files... not very terse. Am I missing an Xtend or a Guice trick to make this work well?

Answer 1

You could use a closure to implement the module interface:

injector = Guice.createInjector [ bind(typeof(SomeType)).to(typeof(AnImplementation)) ]

However, this will not solve the problem for the type literals. You'd have to use Java for that one, but I think it will not hurt.

Answer 2

what about intoducing a real class instead of a anonymous inner one?

Answer 3

On a related note, you can use an Xtend closure to implement Guice's Provider interface.

For example, calling IResourceScopeCache.get in Java:

@Inject
private IResourceScopeCache cache;

public EvaluatedResource getEvaluatedResource(EObject object) {
    final Resource resource = object.eResource();
    return cache.get("key", resource, new Provider<Object>() {
        public Object get() {
            return evaluate(resource);
        }
    });
}

public EvaluatedResource evaluate(Resource resource) {
    ...; // create EvaluatedResource evaluatedResource
    return evaluatedResource; // return it
}

in Xtend becomes:

@Inject
IResourceScopeCache cache

def getEvaluatedResource(EObject object) {
    val resource = object.eResource
    cache.get("key", resource, [|evaluate(resource)])
}

def evaluate(Resource resource) {
    ... // create EvaluatedResource evaluatedResource
    evaluatedResource // return it
}

The trick is that [|...] is a function with zero parameters, in this case Provider.get().