Auto Delegate

Generate (as a super-class) implementations of the delegation pattern, loosely modeled after Kotlin's built-in delegation.

A class annotated with @AutoDelegate will have an AutoDelegate class generated that will implement the given interfaces by delegating them to an instance passed to the constructor. The generated class is meant to be the superclass of the annotated class. A superclass of the annotated class can be given to the annotation as well. The annotated class can freely override any of the generated methods

In the below example, the AutoDelegate annotation processor generates the AutoDelegate_Derived class that implements the Base interface by delegating to a Base instance passed to its constructor.

interface Base {
    void print();
}

class BaseImpl implements Base {
  private final int x;

  BaseImpl(int x) {
    this.x = x;
  }

  @Override void print() {
    System.out.println(x);
  }
}

@AutoDelegate(@Delegate(value = Base.class, name = "base"))
class Derived extends AutoDelegate_Derived {
  Derived(Base b) {
    super(b);
  }
}

class Main {
  public static void main(String[] args) {
    var b = new BaseImpl(10);
    new Derived(b).print();
  }
}

The AutoDelegate_Derived generated class looks more or less like the following

abstract class AutoDelegate_Derived implements Base {
  protected final Base base;

  AutoDelegate_Derived(Base base) {
    this.base = base;
  }

  @Override
  public void print() {
    this.base.print();
  }
}

TODO

Ignore non-visible constructors of the superclass
Handle generics (generic interfaces, generic superclass, generic methods)
Handle methods contributed by several interfaces and/or inherited from the superclass
More user-friendly errors for actually-private nested classes (non-private classes nested in a private class)

tbroyer/auto-delegate

Auto Delegate

TODO