Various framework code based on Guice needs to bind a parameterized type where
some of the type arguments contain in-scope type variables, which obviously
must be reified by existing type tokens of some kind. A contrived example:
abstract class FancyModule extends AbstractModule {
<T> AnnotatedBindingBuilder<List<T>> bindListOf(Class<T> classT) {
TypeLiteral<List<T>> tl_LT = /* ??? */;
return bind(tl_LT);
}
}
One would like to just do:
TypeLiteral<List<T>> tl_LT = new TypeLiteral<List<T>>() {};
but there is no way to pass in classT, so Guice will inevitably raise the error
"List<T> cannot be used as a key; It is not fully specified" when it discovers
the information is missing. The following works, but is clunky and incurs an
unchecked warning:
TypeLiteral<List<T>> tl_LT = (TypeLiteral<List<T>>) \
TypeLiteral.get(Types.newParameterizedType(List.class, classT));
I propose to introduce new variants of the TypeLiteral class that take
additional type parameters and corresponding TypeLiteral tokens, like this:
abstract class TypeLiteralV1<T, A> extends TypeLiteral<T> {
protected TypeLiteralV1(TypeLiteral<A> tokA) { ... }
}
TypeLiteral<T> tl_T = TypeLiteral.get(classT);
TypeLiteral<List<T>> tl_LT = new TypeLiteralV1<List<T>, T>(tlT) {};
The implementation then reads the anonymous subclass's extends declaration
"TypeLiteralV1<List<T>, T>" to learn that T is reified by tl_T, and thus uses
tl_T to construct a reification of List of whatever T actually is.
I have sample code for this construction from a Google internal project, and
the code has just been approved for open-source release. I will be submitting
a patch based on this code to Guice.
Original issue reported on code.google.com by mattmccu...@google.com on 30 Sep 2011 at 10:37
Original issue reported on code.google.com by
mattmccu...@google.com
on 30 Sep 2011 at 10:37