*     visit(t.getGenericComponentType());
 *   }
 *   protected void visitTypeVariable(TypeVariable<?> t) {
 *     throw new IllegalArgumentException("Cannot contain type variable.");
 *   }
 *   protected void visitWildcardType(WildcardType t) {
 *     throw new IllegalArgumentException("Cannot contain wildcard type.");
 *   }
 * }.visit(type);
 * }
 *

    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> typeVariable) {
        mappings.put(new TypeVariableKey(typeVariable), to);
      }

      @Override
      void visitWildcardType(WildcardType fromWildcardType) {
        if (!(to instanceof WildcardType)) {
          return; // okay to say <?> is anything
        }
        WildcardType toWildcardType = (WildcardType) to;

    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> t) {
        result.set(subtypeOfComponentType(t.getBounds()));
      }

      @Override
      void visitWildcardType(WildcardType t) {
        result.set(subtypeOfComponentType(t.getUpperBounds()));
      }

      @Override
      void visitGenericArrayType(GenericArrayType t) {
        result.set(t.getGenericComponentType());

        throw new IllegalArgumentException(
            runtimeType + "contains a type variable and is not safe for the operation");
      }

      @Override
      void visitWildcardType(WildcardType type) {
        visit(type.getLowerBounds());
        visit(type.getUpperBounds());
      }

      @Override
      void visitParameterizedType(ParameterizedType type) {