# Dependencies { #dependencies }

**FastAPI** has a very powerful but intuitive **<dfn title="also known as components, resources, providers, services, injectables">Dependency Injection</dfn>** system.

It is designed to be very simple to use, and to make it very easy for any developer to integrate other components with **FastAPI**.

## What is "Dependency Injection" { #what-is-dependency-injection }

     * The detailed error log or stack trace for the failure.
     * This field contains the full error information for debugging purposes.
     */
    public String errorLog;

    /**
     * The number of times this URL has failed.
     * This is a required field that tracks repeated failures for the same URL.
     */
    @Required
    @ValidateTypeFailure
    public String errorCount;

    /**

    val writer = DerWriter(buffer)
    toDer(writer, value)
    return buffer.readByteString()
  }

  /**
   * Returns an adapter that expects this value wrapped by another value. Typically this occurs
   * when a value has both a context or application tag and a universal tag.
   *
   * Use this for EXPLICIT tag types:
   *
   * ```
   * [5] EXPLICIT UTF8String
   * ```
   *

    SUBMAP,
    DESCENDING;

    @Override
    public Set<Feature<? super @Nullable Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  /**
   * Creates a suite whose map has some elements filtered out of view.
   *
   * <p>Because the map may be ascending or descending, this test must derive the relative order of
   * these extreme values rather than relying on their regular sort ordering.
   */

     *
     * @param reader
     *            the {@link BufferedReader} (must not be {@literal null})
     * @return a line of text, or {@literal null} if the end of the stream has been reached
     * @see BufferedReader#readLine()
     */
    public static String readLine(final BufferedReader reader) {
        assertArgumentNotNull("reader", reader);

        try {

	if len(f.cachedTags) == 0 {
		return true
	}

	parsedTags, err := tags.ParseObjectTags(userTags)
	if err != nil {
		return false
	}

	tagsMap := parsedTags.ToMap()

	// This filter has tags configured but this object
	// does not have any tag, skip this object
	if len(tagsMap) == 0 {
		return false
	}

	// Both filter and object have tags, find a match,
	// skip this object otherwise

     * Asserts that the expected completion time has passed (and not "too much" time beyond that).
     */
    void assertCompletionExpected() {
      assertAtLeastTimePassed(stopwatch, expectedCompletionWaitMillis);
      assertTimeNotPassed(stopwatch, expectedCompletionWaitMillis + LONG_DELAY_MS);
    }

    /**
     * Asserts that at least {@code timeout} has passed but the expected completion time has not.
     */

     * <p>
     * Specifically, if the SID has
     * been resolved and it is not a domain SID or builtin account,
     * the full DOMAIN\name form of the account will be
     * returned (e.g. MYDOM\alice or MYDOM\Domain Users).
     * If the SID has been resolved but it is is a domain SID,
     * only the domain name will be returned (e.g. MYDOM).
     * If the SID has been resolved but it is a builtin account,

    /**
     * Retrieves the configuration for the specified field name.
     *
     * @param fieldName the name of the field to get configuration for
     * @return an OptionalThing containing the Config if the field exists and has a non-blank value,
     *         otherwise an empty OptionalThing
     */
    public OptionalThing<Config> getConfig(final String fieldName) {
        final String value = params.get(fieldName);

    if (uriStripped) {
      if (uri.toString() != component.urlString("")) {
        fail("Encoding $component $codePoint using $encoding")
      }
      return
    }

    // If the URI has more escaping than the HttpURL, check that the decoded values still match.
    val uriEscaped = uriEscapedCodePoints.indexOf(codePointString) != -1
    if (uriEscaped) {
      if (uri.toString() == httpUrl.toString()) {