Is there a way to refer to the current type with a type variable?

Question

Suppose I\'m trying to write a function to return an instance of the current type. Is there a way to make T refer to the exact subtype (so T should

Answer 1

Manifold provides Java with the self type via the @Self annotation.

The simple case:

public class Foo {
  public @Self Foo getMe() {
    return this;
  }
}

public class Bar extends Foo {
}

Bar bar = new Bar().getMe(); // Voila!

Use with generics:

public class Tree {
  private List<Tree> children;

  public List<@Self Tree> getChildren() {
    return children;
  }
}

public class MyTree extends Tree {
}

MyTree tree = new MyTree();
...
List<MyTree> children = tree.getChildren(); // :)  

Use with extension methods:

package extensions.java.util.Map;
import java.util.Map;
public class MyMapExtensions {
  public static <K,V> @Self Map<K,V> add(@This Map<K,V> thiz, K key, V value) {
    thiz.put(key, value);
    return thiz;
  }
}

// `map` is a HashMap<String, String>
var map = new HashMap<String, String>()
  .add("bob", "fishspread")
  .add("alec", "taco")
  .add("miles", "mustard");