Now we are going to update our dependencies.

We want to get the `current_user` *only* if this user is active.

So, we create an additional dependency `get_current_active_user` that in turn uses `get_current_user` as a dependency.

Both of these dependencies will just return an HTTP error if the user doesn't exist, or if is inactive.

* etc.

## Simple and Powerful { #simple-and-powerful }

Although the hierarchical dependency injection system is very simple to define and use, it's still very powerful.

You can define dependencies that in turn can define dependencies themselves.

    assertThat(pool.connectionCount()).isEqualTo(1)

    // All other connections created will expire sooner
    routePlanner.defaultConnectionIdleAtNanos = expireSooner

    // Turn it into an http/2 connection that supports 5 concurrent streams
    // which can satisfy a larger policy
    val connection = routePlanner.plans.first().connection
    val http2Connection = connectHttp2(peer, connection, 5)

doubt that it had a VERY turn-up nose, much more like a snout
than a real nose; also its eyes were getting extremely small for
a baby:  altogether Alice did not like the look of the thing at
all.  `But perhaps it was only sobbing,' she thought, and looked
into its eyes again, to see if there were any tears.

  No, there were no tears.  `If you're going to turn into a pig,

 * [HTTP Public Key Pinning (HPKP)][rfc_7469] or SHA-1 base64 hashes as in Chromium's
 * [static certificates][static_certificates].
 *
 * ## Setting up Certificate Pinning
 *
 * The easiest way to pin a host is turn on pinning with a broken configuration and read the
 * expected configuration when the connection fails. Be sure to do this on a trusted network, and
 * without man-in-the-middle tools like [Charles][charles] or [Fiddler][fiddler].
 *

				}
				for i+1 < len(printed) && (printed[i+1] == ' ' || printed[i+1] == '\t') {
					i++
				}
				continue
			}
			buf = append(buf, c)
		}

		f := strings.Fields(string(buf))

		// Turn relative (PC) into absolute (PC) automatically,
		// so that most branch instructions don't need comments
		// giving the absolute form.
		if len(f) > 0 && strings.Contains(printed, "(PC)") {
			index := len(f) - 1

   *       for every closeable object this step creates in order to capture it for later closing.
   *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
   *       ClosingFuture} call {@link #from(ListenableFuture)}.
   *   <li>In case this step doesn't create new closeables, you can adapt an API that returns a

          <show>package</show>
        </configuration>
      </plugin>
      <!-- Disable "normal" testing, which doesn't work for GWT tests. -->

And all of them can use `yield`.

In this case `dependency_c`, to execute its exit code, needs the value from `dependency_b` (here named `dep_b`) to still be available.

And, in turn, `dependency_b` needs the value from `dependency_a` (here named `dep_a`) to be available for its exit code.

{* ../../docs_src/dependencies/tutorial008_an_py39.py hl[18:19,26:27] *}

for race-free programs are equivalent to the ones in that work.
</p>

<p>
The memory model describes the requirements on program executions,
which are made up of goroutine executions,
which in turn are made up of memory operations.
</p>

<p>
A <i>memory operation</i> is modeled by four details:
</p>
<ul>
	<li>its kind, indicating whether it is an ordinary data read, an ordinary data write,