Generic with Variable Type Arguments

Question

I want to do something like

public interface Foo<R, P...> {
    public R bar(P...) {/*misc*/}
}

to get an array of types to use in my bound implementation. Is this possible in java?

Varargs is designed to let me have any number of arguments of a given class.

I want to use it (or something similar) to have my method accept several arguments, each of which is a member of a given different class. These classes are defined when the generic is bound.

I aware there are work arounds, but is there a type-safe way to do this?

Answer 1

Since you apparently want to be able to make bar take multiple parameters of different types (something varargs are not used for), I'd suggest making it instead take a single parameter. You can then make that single parameter be a container that holds each of the individual "parameters" you want to use.

In general, it would be best to make a class for each set of parameters you want to use with this method so that you have good names for each of the objects it contains. However, you could also do something like creating a series of tuple types (such as Pair) to use as holders.

Here's an example:

public class Foo<R, P> {
  /*
   * Not sure how you intend to provide any kind of implementation
   * here since you don't know what R or P are.
   */
  public R bar(P parameters) { ... }
}

public class SomeFoo extends Foo<SomeResult, Pair<Baz, Bar>> {
  public SomeResult bar(Pair<Baz, Bar> parameters) { ... }
}

SomeFoo foo = ...
SomeResult result = foo.bar(Pair.of(baz, bar));