Clojure Q&A - Recent questions tagged interface

Could deftype allow for overriding methods?

Sat, 13 Aug 2022 16:52:31 +0000

Currently implementing a custom java.util.Iterator with the usual deftype form like

(deftype MyIterator []
  Iterator
  (hasNext [this]
    (my-custom-code))
  (next [this]
    (my-custom-code))
)

But I'd like to override the forEachRemaining default method on Iterator:

default void forEachRemaining(Consumer<? super E> action) {
    Objects.requireNonNull(action);
    while (hasNext())
        action.accept(next());
}

... with a more performant/specialized implementation. Perhaps I would even want to implement the by-default unimplemented remove:

default void remove() {
    throw new UnsupportedOperationException("remove");
}

But deftype does not allow for overriding methods. Is this a fundamental limitation or just something that hasn't been done (probably because Clojure predates default methods in java 8)? Anyways as a language whose philosophy is to embrace the the host, this would come in highly useful for using/integrating with java interfaces.

How to call java method with interface as parameters?

Fri, 08 May 2020 04:37:31 +0000

Here's my sample code.
Thanks.

// Java code
interface IFace {
  String message();
}
class A implements IFace {
  @Override message () { return "Hello A!"};
}
class B implements IFace {
  @Override message () { return "Hello B!"};
}
class PrintHello {
  static void print (IFace msg) {
    if (msg instanceof A) { ... } else { ... }
  }
}

; Clojure code

(def a (A.))
(. PrintHello (print a))

Replacing core interfaces with protocols

Sun, 04 Aug 2019 16:04:40 +0000

Currently IFn, IDererf etc implemented as interfaces in clojure but these are protocols in clojurescript.
Are there any plans to fix this mismatch?