It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you:

{* ../../docs_src/openapi_callbacks/tutorial001.py hl[9:13,36:53] *}

/// tip

    val index = serialTaskQueue.indexOfFirst { it.isReady() }
    if (index == -1) return null

    val nextTask = serialTaskQueue.removeAt(index)
    currentTask = nextTask
    contextSwitchCount++
    nextTask.start()
    return nextTask
  }

  private interface SerialTask {
    /** Returns true if this task is ready to start. */
    fun isReady() = true

    List<String> alreadyThere = Lists.newArrayList("already", "there");

    boolean changed = Iterators.addAll(alreadyThere, Iterators.<String>emptyIterator());
    assertThat(alreadyThere).containsExactly("already", "there").inOrder();
    assertFalse(changed);
  }

  public void testAddAllToList() {
    List<String> alreadyThere = Lists.newArrayList("already", "there");

   */
  public final void visit(@Nullable Type... types) {
    for (Type type : types) {
      if (type == null || !visited.add(type)) {
        // null owner type, or already visited;
        continue;
      }
      boolean succeeded = false;
      try {
        if (type instanceof TypeVariable) {
          visitTypeVariable((TypeVariable<?>) type);

### Return values { #return-values }

And they can return values or not, the values won't be used.

So, you can reuse a normal dependency (that returns a value) you already use somewhere else, and even though the value won't be used, the dependency will be executed:

{* ../../docs_src/dependencies/tutorial006_an_py39.py hl[11,16] *}

            "The filename, directory name, or volume label syntax is incorrect.", "The directory is not empty.",
            "Cannot create a file when that file already exists.", "All pipe instances are busy.", "The pipe is being closed.",
            "No process is on the other end of the pipe.", "More data is available.", "This user account has expired.",

            "The filename, directory name, or volume label syntax is incorrect.", "The directory is not empty.",
            "Cannot create a file when that file already exists.", "All pipe instances are busy.", "The pipe is being closed.",
            "No process is on the other end of the pipe.", "More data is available.", "This user account has expired.",

        } else // don't truncate the file
        if ((flags & SmbFile.O_CREAT) == SmbFile.O_CREAT) {
            // create it if necessary
            if ((flags & SmbFile.O_EXCL) == SmbFile.O_EXCL) {
                // fail if already exists
                openFunction = OPEN_FN_CREATE | OPEN_FN_FAIL_IF_EXISTS;
            } else {
                openFunction = OPEN_FN_CREATE | OPEN_FN_OPEN;
            }
        } else {

# About FastAPI versions { #about-fastapi-versions }

**FastAPI** is already being used in production in many applications and systems. And the test coverage is kept at 100%. But its development is still moving quickly.

New features are added frequently, bugs are fixed regularly, and the code is still continuously improving.

		Code:           "XMinioAdminBucketRemoteAlreadyExists",
		Description:    "The remote target already exists",
		HTTPStatusCode: http.StatusBadRequest,
	},
	ErrBucketRemoteLabelInUse: {
		Code:           "XMinioAdminBucketRemoteLabelInUse",
		Description:    "The remote target with this label already exists",
		HTTPStatusCode: http.StatusBadRequest,
	},
	ErrBucketRemoteRemoveDisallowed: {