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)

                "Method com.example.Source.baz(): From non-null returning to null-unmarked returning breaking change.",
            )
            assertHasNoWarning()
            assertHasNoInformation()
        }
    }

    @Test
    fun `from null-unmarked returning to non-null returning is not breaking`() {

                "Method com.example.Source.foo(): From non-null returning to null returning breaking change."
            )
            assertHasNoWarning()
            assertHasNoInformation()
        }
    }

    @Test
    fun `from non-null array element returning to null returning is breaking`() {

        checkNotBinaryCompatibleJava(
            v1 = """

// only sqlite, postgres, gaussdb, sqlserver support returning
func TestSoftDeleteReturning(t *testing.T) {
	if DB.Dialector.Name() != "sqlite" && DB.Dialector.Name() != "postgres" && DB.Dialector.Name() != "gaussdb" && DB.Dialector.Name() != "sqlserver" {
		return
	}

	users := []*User{
		GetUser("delete-returning-1", Config{}),
		GetUser("delete-returning-2", Config{}),
		GetUser("delete-returning-3", Config{}),
	}
	DB.Create(&users)

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.

                errors << "From non-null returning to null returning breaking change"
            } else if (oldNullability == Nullability.NON_NULL && newNullability == Nullability.UNMARKED) {
                errors << "From non-null returning to null-unmarked returning breaking change"
            } else if (oldNullability == Nullability.UNMARKED && newNullability == Nullability.NULLABLE) {

              }
            },
            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*.

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.