* recursion by calling {@link #visit} for any {@code Type} while visitation is in progress. For
 * example, this can be used to reject wildcards or type variables contained in a type as in:
 *
 * {@snippet :
 * new TypeVisitor() {
 *   protected void visitParameterizedType(ParameterizedType t) {
 *     visit(t.getOwnerType());
 *     visit(t.getActualTypeArguments());
 *   }
 *   protected void visitGenericArrayType(GenericArrayType t) {

  }

  private static void populateTypeMappings(
      Map<TypeVariableKey, Type> mappings, Type from, Type to) {
    if (from.equals(to)) {
      return;
    }
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> typeVariable) {
        mappings.put(new TypeVariableKey(typeVariable), to);
      }

      @Override

  }

  private static void populateTypeMappings(
      Map<TypeVariableKey, Type> mappings, Type from, Type to) {
    if (from.equals(to)) {
      return;
    }
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> typeVariable) {
        mappings.put(new TypeVariableKey(typeVariable), to);
      }

      @Override

  }

  static @Nullable Type getComponentType(Type type) {
    checkNotNull(type);
    AtomicReference<@Nullable Type> result = new AtomicReference<>();
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> t) {
        result.set(subtypeOfComponentType(t.getBounds()));
      }

      @Override
      void visitWildcardType(WildcardType t) {

  }

  static @Nullable Type getComponentType(Type type) {
    checkNotNull(type);
    AtomicReference<@Nullable Type> result = new AtomicReference<>();
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> t) {
        result.set(subtypeOfComponentType(t.getBounds()));
      }

      @Override
      void visitWildcardType(WildcardType t) {