/** Call this in a {@link TestSubtype} public method asserting subtype relationship. */
  final <T> T isSubtype(T sub) {
    Type returnType = method.getGenericReturnType();
    Type paramType = getOnlyParameterType();
    TestSubtype spec = method.getAnnotation(TestSubtype.class);
    assertWithMessage("%s is subtype of %s", paramType, returnType)
        .that(TypeToken.of(paramType).isSubtypeOf(returnType))

  /** Call this in a {@link TestSubtype} public method asserting subtype relationship. */
  final <T> T isSubtype(T sub) {
    Type returnType = method.getGenericReturnType();
    Type paramType = getOnlyParameterType();
    TestSubtype spec = method.getAnnotation(TestSubtype.class);
    assertWithMessage("%s is subtype of %s", paramType, returnType)
        .that(TypeToken.of(paramType).isSubtypeOf(returnType))

With **FastAPI**, you can define, validate, document, and use arbitrarily deeply nested models (thanks to Pydantic).

## List fields { #list-fields }

You can define an attribute to be a subtype. For example, a Python `list`:

{* ../../docs_src/body_nested_models/tutorial001_py310.py hl[12] *}

This will make `tags` be a list, although it doesn't declare the type of the elements of the list.

                            message["content-type"] = content_type_value
                            if message.get_content_maintype() == "application":
                                subtype = message.get_content_subtype()
                                if subtype == "json" or subtype.endswith("+json"):
                                    json_body = await request.json()
                        if json_body != Undefined:

   * V>} to a {@code NavigableMap<K, V>}. If it permitted this, the returned map's {@code
   * comparator()} method might return a {@code Comparator<? extends K>}, which works only on a
   * particular subtype of {@code K}, but promise that it's a {@code Comparator<? super K>}, which
   * must work on any type of {@code K}.
   *
   * @param map the navigable map for which an unmodifiable view is to be returned

     */
    protected SsoAuthenticator getAuthenticator() {
        String ssoType = getSsoType();
        // Backward compatibility: map legacy "aad" (Azure AD) to "entraid" (Entra ID)
        if ("aad".equals(ssoType)) {
            ssoType = "entraid";
        }
        final String name = ssoType + "Authenticator";
        if (ComponentUtil.hasComponent(name)) {

 * detailed at {@link ImmutableCollection}.
 *
 * <p><b>Warning:</b> avoid <i>direct</i> usage of {@link ImmutableMultimap} as a type (as with
 * {@link Multimap} itself). Prefer subtypes such as {@link ImmutableSetMultimap} or {@link
 * ImmutableListMultimap}, which have well-defined {@link #equals} semantics, thus avoiding a common
 * source of bugs and confusion.
 *

        return methodParametersFromSignature(methodInSubClass) == methodParametersFromSignature(method)
            // Subclass can override method return type
            && methodInSubClass.returnType.subtypeOf(method.returnType)
    }

    /**
     * Returns method parameters from method signature, e.g. "(Ljava/lang/String;I)V" -> "(Ljava/lang/String;I)"
     */

 * detailed at {@link ImmutableCollection}.
 *
 * <p><b>Warning:</b> avoid <i>direct</i> usage of {@link ImmutableMultimap} as a type (as with
 * {@link Multimap} itself). Prefer subtypes such as {@link ImmutableSetMultimap} or {@link
 * ImmutableListMultimap}, which have well-defined {@link #equals} semantics, thus avoiding a common
 * source of bugs and confusion.
 *

     * @return the parsed sitemap set
     */
    protected SitemapSet parseTextSitemaps(final InputStream in) {
        final SitemapSet sitemapSet = new SitemapSet();
        sitemapSet.setType(SitemapSet.URLSET);

        try {
            final BufferedReader br = new BufferedReader(new InputStreamReader(in, Constants.UTF_8));
            String line;
            while ((line = br.readLine()) != null) {