We make changes to Guava's public [APIs][], including adding new APIs, very
carefully. Because of this, if you're interested in seeing a new feature in
Guava, the best approach is to create an [issue][] (or comment on an existing
issue if there is one) requesting the feature and describing specific use cases
for it.

If the feature has merit, it will go through a thorough process of API design
and review. Any code should come after this.

import com.google.common.collect.testing.SetTestSuiteBuilder;
import com.google.common.collect.testing.TestStringSetGenerator;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;
import com.google.common.collect.testing.features.Feature;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import junit.framework.Test;

import com.google.common.collect.testing.SetTestSuiteBuilder;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.Feature;
import com.google.common.collect.testing.features.MapFeature;
import com.google.common.collect.testing.google.DerivedGoogleCollectionGenerators.BiMapValueSetGenerator;

@GwtCompatible
public enum MultimapFeature implements Feature<Multimap> {
  VALUE_COLLECTIONS_SUPPORT_ITERATOR_REMOVE;

  private final Set<Feature<? super Multimap>> implied;

  MultimapFeature(Feature<? super Multimap>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override
  public Set<Feature<? super Multimap>> getImpliedFeatures() {
    return implied;
  }

  }

  enum ExampleDerivedFeature implements Feature<ExampleDerivedInterface> {
    DERIVED_FEATURE_1,
    DERIVED_FEATURE_2(ExampleBaseFeature.BASE_FEATURE_1),
    DERIVED_FEATURE_3,

    COMPOUND_DERIVED_FEATURE(
        DERIVED_FEATURE_1, DERIVED_FEATURE_2, ExampleBaseFeature.BASE_FEATURE_2);

    private Set<Feature<? super ExampleDerivedInterface>> implied;

    ExampleDerivedFeature(Feature<? super ExampleDerivedInterface>... implied) {

@GwtCompatible
public enum SetFeature implements Feature<Set> {
  GENERAL_PURPOSE(CollectionFeature.GENERAL_PURPOSE);

  private final Set<Feature<? super Set>> implied;

  SetFeature(Feature<? super Set>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override
  public Set<Feature<? super Set>> getImpliedFeatures() {
    return implied;
  }

  private final Set<Feature<? super List>> implied;

  ListFeature(Feature<? super List>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override
  public Set<Feature<? super List>> getImpliedFeatures() {
    return implied;
  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {

    abstract Map<String, String> wrap(HashMap<String, String> map);
  }

  private static TestSuite wrappedHashMapTests(
      WrappedHashMapGenerator generator, String name, Feature<?>... features) {
    List<Feature<?>> featuresList = Lists.newArrayList(features);
    Collections.addAll(
        featuresList,
        MapFeature.GENERAL_PURPOSE,
        CollectionFeature.SUPPORTS_ITERATOR_REMOVE,
        CollectionSize.ANY);

    List<Feature<?>> features = new ArrayList<>();
    features.add(NoRecurse.SUBMAP);
    features.addAll(parentBuilder.getFeatures());

    return newBuilderUsing(delegate, to, from)
        .named(parentBuilder.getName() + " subMap " + from + "-" + to)
        .withFeatures(features)
        .suppressing(parentBuilder.getSuppressedTests())

  /**
   * For documenting collections that support no optional features, such as {@link
   * java.util.Collections#emptySet}
   */
  NONE;

  private final Set<Feature<? super Collection>> implied;

  CollectionFeature(Feature<? super Collection>... implied) {
    this.implied = Helpers.copyToSet(implied);
  }

  @Override
  public Set<Feature<? super Collection>> getImpliedFeatures() {
    return implied;
  }