import java.util.Map;
import javax.annotation.CheckForNull;

/**
 * A {@link MapIteratorCache} that adds additional caching. In addition to the caching provided by
 * {@link MapIteratorCache}, this structure caches values for the two most recently retrieved keys.
 *
 * @author James Sexton
 */
@ElementTypesAreNonnullByDefault
final class MapRetrievalCache<K, V> extends MapIteratorCache<K, V> {

import java.util.Optional;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for <a
 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
 * whose edges are unique objects.
 *
 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
 *

  </parent>

  <groupId>inheritance</groupId>
  <artifactId>inheritance</artifactId>
  <version>11-SNAPSHOT</version>
  <name>Model urls inheritance test child</name>
  <description>Flat directory structure case: module = ../child-artifact-id + child directory path == child-artifact-id</description>

  <!-- 5 inherited urls with ../${project.artifactId} added to parent -->

  <groupId>inheritance</groupId>
  <artifactId>parent</artifactId>
  <version>11-SNAPSHOT</version>

  <name>Model urls inheritance test parent</name>
  <description>Flat directory structure case: module = ../child-artifact-id + child directory path == child-artifact-id</description>

  <modules>
    <module>../inheritance</module>
  </modules>

  <!-- 5 urls in the pom will be inherited with path added -->

import java.util.Optional;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for <a
 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
 * whose edges have associated non-unique values.
 *
 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
 *

  </parent>

  <groupId>inheritance</groupId>
  <artifactId>child-artifact-id</artifactId>
  <version>11-SNAPSHOT</version>
  <name>Model urls inheritance test child</name>
  <description>Flat directory structure case: module = ../child directory path + child directory path != child-artifact-id</description>

  <!-- 5 inherited urls with ../${project.artifactId} added to parent -->

In a real application, you probably would have your tests in a different file.

And your **FastAPI** application might also be composed of several files/modules, etc.

### **FastAPI** app file

Let's say you have a file structure as described in [Bigger Applications](bigger-applications.md){.internal-link target=_blank}:

```
.
├── app
│   ├── __init__.py
│   └── main.py
```

In the file `main.py` you have your **FastAPI** app:

   * code would be responsible for populating a "real" {@code T} (which might still be the value
   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
   * nullness analysis might not understand that the field has been populated. To avoid that problem
   * without having to add {@code @SuppressWarnings}, the code can call this method.
   *

   * code would be responsible for populating a "real" {@code T} (which might still be the value
   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
   * nullness analysis might not understand that the field has been populated. To avoid that problem
   * without having to add {@code @SuppressWarnings}, the code can call this method.
   *

package once

import (
	"context"
	"sync"
	"sync/atomic"
)

// Inspired from Golang sync.Once but it is only marked
// initialized when the provided function returns nil.

// Init represents the structure.
type Init struct {
	done uint32
	m    sync.Mutex
}

// Do is similar to sync.Once.Do - makes one successful
// call to the function. ie, it invokes the function
// if it is not successful yet.