return s.v
	default:
		return nil
	}
}

// IsSet will return whether the singleton has been set.
func (s *Singleton[T]) IsSet() bool {
	select {
	case <-s.set:
		return true
	default:
		return false
	}
}

// Set the value and unblock all Get requests.
// This may only be called once, a second call will panic.
func (s *Singleton[T]) Set(v *T) {
	s.v = v
	close(s.set)

		return left.After(right)
	case opGte:
		return left.After(right) || left.Equal(right)
	case opEq:
		return left.Equal(right)
	case opIneq:
		return !left.Equal(right)
	}
	// This case does not happen
	return false

    return MoreObjects.firstNonNull(asMap().remove(key), unmodifiableEmptyCollection());
  }

  Collection<V> unmodifiableEmptyCollection() {
    // These return false, rather than throwing a UOE, on remove calls.
    return (unfiltered instanceof SetMultimap)
        ? Collections.<V>emptySet()
        : Collections.<V>emptyList();
  }

  @Override
  public void clear() {

      assertTrue(Thread.holdsLock(mutex));
      return delegate().headMap(toKey, inclusive);
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public @Nullable Entry<K, V> higherEntry(K key) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().higherEntry(key);
    }

    @Override

            return false;
        }

        if ( ( this.server.scapabilities & SmbConstants.CAP_EXTENDED_SECURITY ) != SmbConstants.CAP_EXTENDED_SECURITY
                && this.server.encryptionKeyLength != 8 && ctx.getConfig().getLanManCompatibility() == 0 ) {
            log.warn("Unexpected encryption key length: " + this.server.encryptionKeyLength);
            return false;
        }

	if e.selectAST.Where == nil {
		return true, nil
	}
	value, err := e.selectAST.Where.evalNode(input, e.tableAlias)
	if err != nil {
		return false, err
	}

	b, ok := value.ToBool()
	if !ok {
		err = fmt.Errorf("WHERE expression did not return bool")
		return false, err
	}

	return b, nil
}

// AggregateRow - aggregates the input record. Applies only to
// aggregation queries.

                // ignore this task
                task.setEnabled(false);
                return;
            }

            task.setExecutionMode(ExecutionMode.OUT_OF_PROCESS);
            task.outputOptions(options -> {
                options.setSeparateOutputDirs(false);
                options.setBackends(singletonList("html5"));
            });

            return null;
        });
        stopwordsService.store(body.dictId, entity);
        return asJson(
                new ApiResult.ApiUpdateResponse().id(String.valueOf(entity.getId())).created(false).status(ApiResult.Status.OK).result());
    }

    // DELETE /api/admin/dict/stopwords/setting/{dictId}/{id}
    @Execute
    public JsonResponse<ApiResult> delete$setting(final String dictId, final long id) {

            new CountDownLatch(1).await(); // the interrupt will wake us up
            return null;
          }

          @Override
          boolean isDone() {
            return false;
          }

          @Override
          String toPendingString() {
            return "";
          }

          @Override
          void afterRanInterruptiblySuccess(@Nullable Void result) {}

在高级使用场景中，如果不想使用「缓存」值，而是为需要在同一请求的每一步操作（多次）中都实际调用依赖项，可以把 `Depends` 的参数 `use_cache` 的值设置为 `False` :

```Python hl_lines="1"
async def needy_dependency(fresh_value: str = Depends(get_value, use_cache=False)):
    return {"fresh_value": fresh_value}
```

## 小结

千万别被本章里这些花里胡哨的词藻吓倒了，其实**依赖注入**系统非常简单。

依赖注入无非是与*路径操作函数*一样的函数罢了。