@SuppressWarnings({"unchecked"})
        @Override
        protected void fillFeatures(
            Pair<Mention, ClusteredMention> input,
            Counter<Feature> inFeatures,
            Boolean output,
            Counter<Feature> outFeatures) {
          // --Input Features
          for (Object o : ACTIVE_FEATURES) {
            if (o instanceof Class) {
              // (case: singleton feature)
              Option<Double> count = new Option<Double>(1.0);
              Feature feat = feature((Class) o, input, count);
              if (count.get() > 0.0) {
                inFeatures.incrementCount(feat, count.get());
              }
            } else if (o instanceof Pair) {
              // (case: pair of features)
              Pair<Class, Class> pair = (Pair<Class, Class>) o;
              Option<Double> countA = new Option<Double>(1.0);
              Option<Double> countB = new Option<Double>(1.0);
              Feature featA = feature(pair.getFirst(), input, countA);
              Feature featB = feature(pair.getSecond(), input, countB);
              if (countA.get() * countB.get() > 0.0) {
                inFeatures.incrementCount(
                    new Feature.PairFeature(featA, featB), countA.get() * countB.get());
              }
            }
          }

          // --Output Features
          if (output != null) {
            outFeatures.incrementCount(new Feature.CoreferentIndicator(output), 1.0);
          }
        }
        private <E> Feature feature(
            Class<E> clazz, Pair<Mention, ClusteredMention> input, Option<Double> count) {

          // --Variables
          Mention onPrix =
              input.getFirst(); // the first mention (referred to as m_i in the handout)
          Mention candidate =
              input.getSecond().mention; // the second mention (referred to as m_j in the handout)
          Entity candidateCluster =
              input.getSecond().entity; // the cluster containing the second mention

          // --Features:w
          if (clazz.equals(Feature.ExactMatch.class)) {
            // (exact string match)
            return new Feature.ExactMatch(onPrix.gloss().equals(candidate.gloss()));
          } else if (clazz.equals(Feature.SentenceDist.class)) {
            return new Feature.SentenceDist(
                Math.abs(
                    onPrix.doc.indexOfMention(onPrix) - candidate.doc.indexOfMention(candidate)));
          } else if (clazz.equals(Feature.MentionDist.class)) {
            return new Feature.MentionDist(
                Math.abs(
                    onPrix.doc.indexOfSentence(onPrix.sentence)
                        - candidate.doc.indexOfSentence(candidate.sentence)));
          } else if (clazz.equals(Feature.EitherHeadWordPronoun.class)) {
            return new Feature.EitherHeadWordPronoun(
                Pronoun.isSomePronoun(onPrix.gloss()) || Pronoun.isSomePronoun(candidate.gloss()));
          } else if (clazz.equals(Feature.CandidateNERTag.class)) {
            return new Feature.CandidateNERTag(candidate.headToken().nerTag());
          } else if (clazz.equals(Feature.CandidateSpeaker.class)) {
            return new Feature.CandidateSpeaker(candidate.headToken().speaker());
          } else if (clazz.equals(Feature.FixedSpeaker.class)) {
            return new Feature.FixedSpeaker(onPrix.headToken().speaker());
          } else if (clazz.equals(Feature.HeadWordMatch.class)) {
            return new Feature.HeadWordMatch(onPrix.equals(candidate.headWord()));
          } else if (clazz.equals(Feature.HeadWordLemmaMatch.class)) {
            return new Feature.HeadWordLemmaMatch(
                onPrix.headToken().lemma().equals(candidate.headToken().lemma()));
          } else if (clazz.equals(Feature.FixedNERTag.class)) {
            return new Feature.FixedNERTag(onPrix.headToken().nerTag());
          } else if (clazz.equals(Feature.SpeakerMatch.class)) {
            return new Feature.SpeakerMatch(
                candidate.headToken().speaker().equals(onPrix.headToken().speaker()));
          } else if (clazz.equals(Feature.NERTagMatch.class)) {
            return new Feature.NERTagMatch(
                candidate.headToken().nerTag().equals(onPrix.headToken().nerTag()));
          } else if (clazz.equals(Feature.CandidatePOSTag.class)) {
            return new Feature.CandidatePOSTag(candidate.headToken().posTag());
          } else if (clazz.equals(Feature.FixedPOSTag.class)) {
            return new Feature.FixedPOSTag(onPrix.headToken().posTag());
          } else if (clazz.equals(Feature.GenderMatch.class)) {
            Pair<Boolean, Boolean> match = Util.haveGenderAndAreSameGender(onPrix, candidate);
            boolean finalMatch = (!match.getFirst() || match.getSecond());
            return new Feature.GenderMatch(finalMatch);
          } else if (clazz.equals(Feature.NumberMatch.class)) {
            Pair<Boolean, Boolean> match = Util.haveNumberAndAreSameNumber(onPrix, candidate);
            boolean finalMatch = (!match.getFirst() || match.getSecond());
            return new Feature.NumberMatch(finalMatch);
          }
          //			} else if(clazz.equals(Feature.NewFeature.class) {
          /*
           * TODO: Add features to return for specific classes. Implement calculating values of features here.
           */

          else {
            throw new IllegalArgumentException("Unregistered feature: " + clazz);
          }
        }