Groovy @DelegatesTo and type tokens.

gistfile1.groovy

Handler<T> handler(@DelegatesTo.Target(asType = true) Class<T> type, @DelegatesTo Closure<?> configurer) {
  return new Handler() {
    void handle(T object) {
      configurer.delegate = object
      configure.call(delegate)
    }
  }
}

(parameters[0] instanceof ClassExpression)?parameters[0].type:getType(parameters[0])

That seems doomed for user error. Let's see if we can avoid having to use imperative code.

I understand that {{asType}} doesn't mean "the type that the Class represents"

It did originally, because I was just thinking about type tokens. That is, asType would only work on a Class param (anything else would be an error). In that context, I think the name makes sense. But know that we are talking about something bigger, I agree that the name doesn't make sense.

You would have to map Date to E, then E to V.

I wish I could contribute here, but it's beyond my knowledge.

It seems like:

void someMethod(@DelegatesTo.Target(genericTypeIndex=1) Map<K,V> map, @DelegatesTo Closure<?> closure)

Would cover a lot of use cases if it could be made to work.

Agreed. I'll make some experiments around this.