private abstract static class RawTypeConsistencyTester<T extends Enum<T> & CharSequence> {
    abstract T returningT();

    abstract void acceptT(T t);

    abstract <X extends T> X returningX();

    abstract <X> void acceptX(X x);

    abstract <T2 extends Enum<T2> & CharSequence> T2 returningT2();

    abstract <T2 extends CharSequence & Iterable<T2>> void acceptT2(T2 t2);

  private abstract static class RawTypeConsistencyTester<T extends Enum<T> & CharSequence> {
    abstract T returningT();

    abstract void acceptT(T t);

    abstract <X extends T> X returningX();

    abstract <X> void acceptX(X x);

    abstract <T2 extends Enum<T2> & CharSequence> T2 returningT2();

    abstract <T2 extends CharSequence & Iterable<T2>> void acceptT2(T2 t2);

	expected = updatedAtRe.ReplaceAllString(expected, `"updated_at"=?`)

	// ignore RETURNING "id" (only in PostgreSQL)
	returningRe := regexp.MustCompile(`(?i)RETURNING "id"`)
	actually = returningRe.ReplaceAllString(actually, ``)
	expected = returningRe.ReplaceAllString(expected, ``)

	actually = strings.TrimSpace(actually)
	expected = strings.TrimSpace(expected)

{!../../docs_src/custom_response/tutorial004.py!}
```

In this example, the function `generate_html_response()` already generates and returns a `Response` instead of returning the HTML in a `str`.

By returning the result of calling `generate_html_response()`, you are already returning a `Response` that will override the default **FastAPI** behavior.

# Middleware

You can add middleware to **FastAPI** applications.

A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.

              }
            },
            directExecutor()));
    thingToCancel[0] = serializer.submit(Callables.returning(null), directExecutor());
    results.add(thingToCancel[0]);
    // Enqueue more than enough tasks to force reentrancy.
    for (int i = 0; i < 5; i++) {
      results.add(serializer.submit(Callables.returning(null), directExecutor()));
    }

    manualExecutorTask[0].run();

////

FastAPI will use this return type to:

* **Validate** the returned data.
    * If the data is invalid (e.g. you are missing a field), it means that *your* app code is broken, not returning what it should, and it will return a server error instead of returning incorrect data. This way you and your clients can be certain that they will receive the data and the data shape expected.
* Add a **JSON Schema** for the response, in the OpenAPI *path operation*.

	}

	// mariadb with returning, values will be appended with id map
	if len(values) == beforeLen*2 {
		t.Skipf("This test case skipped, because the db supports returning")
	}

	for i := range values {
		v, ok := values[i]["id"]
		if !ok {
			t.Fatal("failed to create data from map with table, returning map has no primary key")
		}

		var result User

              }
            },
            directExecutor()));
    thingToCancel[0] = serializer.submit(Callables.returning(null), directExecutor());
    results.add(thingToCancel[0]);
    // Enqueue more than enough tasks to force reentrancy.
    for (int i = 0; i < 5; i++) {
      results.add(serializer.submit(Callables.returning(null), directExecutor()));
    }

    manualExecutorTask[0].run();

    assertEquals(1, prepender.times);
  }

  public void testConstructor_returning() throws Exception {
    Invokable<?, Prepender> delegate =
        Prepender.constructor(String.class, int.class).returning(Prepender.class);
    Prepender prepender = delegate.invoke(null, "a", 1);
    assertEquals("a", prepender.prefix);
    assertEquals(1, prepender.times);
  }