How can I write a generic FactoryModuleBuilder?

Question

I'd like to know how to represent a generic version of the following binding that won't fail with xxx cannot be used as a key it is not fully specified

install(new FactoryModuleBuilder().
   implement(new TypeLiteral<SomeClass<T,?>>(){}, 
      new TypeLiteral<SomeOtherClass<T, U>>(){}).
   build(SomeFactory.class);

It seems that the implement method isn't available with a parameterized type parameter.

Answer 1

This is not possible because of the way Guice uses type literal parameters. TypeLiterals require concrete types and, as you see from the exception, cannot accept generic parameters.

To quote @jesse-wilson

Note that Guice doesn't allow bindings for types that aren't fully-qualified. For example, you can bind a Map<String, Integer> but you can't bind a Map<K, V> . https://stackoverflow.com/a/1117878/654187

You can "fully qualify" these bindings as described here: https://stackoverflow.com/a/1120990/654187

But I doubt this is what you want.

The good news is you can still write this factory without assisted injection easily:

public class SomeFactory{
    @Inject
    private SomeDependency someDependency;

    public <T> SomeClass<T, ?> buildSomeClass(T t){
        return new SomeOtherClass<T, Object>(t, someDependency);
    }
}

Answer 2

Alen Vrečko posted :

Imho the best you can do with generics is something like

install(new Assist2<Payment, RealPayment>(PaymentFactory.class){}); or

install(new Assist3<SomeClass<Foo, Bar>, SomeOtherClass<Foo, Bar>, SomeFactory<Foo>(){});

Should be pretty easy to implement this approach. Just look in the source of TypeLiteral.

If you absolutely need type parameters something like:

install(new CustomAssist<Baz>(){}); where

CustomAssist<T> extends Assist<SomeClass<Foo,T>,SomeOtherClass<Foo,Bar>{...

might be possible but not trivial to implement. But a lot of fun.

Answer 3

To follow on from @johncarl

If you are just injecting someDependency then you'll be getting the instance when the factory is created. To make it work like a FactoryModuleBuilder constructed factory you'll need to inject the Injector

public class SomeFactory{
    @Inject
    private Injector injector;

    public <T> SomeClass<T, ?> buildSomeClass(T t) {
        return new SomeOtherClass<T, Object>(t, injector.getInstance(SomeDependency));
    }
}