Class Scopes

core/src/com/google/inject/Scopes.java:32–202

Built-in scope implementations. @author crazybob@google.com (Bob Lee)

 * @author crazybob@google.com (Bob Lee)
 */
public class Scopes {

  private Scopes() {}

  /** One instance per {@link Injector}. Also see {@code @}{@link Singleton}. */
  public static final Scope SINGLETON = new SingletonScope();

  /**
   * No scope; the same as not applying any scope at all. Each time the Injector obtains an instance
   * of an object with "no scope", it injects this instance then immediately forgets it. When the
   * next request for the same binding arrives it will need to obtain the instance over again.
   *
   * <p>This exists only in case a class has been annotated with a scope annotation such as {@link
   * Singleton @Singleton}, and you need to override this to "no scope" in your binding.
   *
   * @since 2.0
   */
  public static final Scope NO_SCOPE =
      new Scope() {
        @Override
        public <T> Provider<T> scope(Key<T> key, Provider<T> unscoped) {
          return unscoped;
        }

        @Override
        public String toString() {
          return "Scopes.NO_SCOPE";
        }
      };

  private static final BindingScopingVisitor<Boolean> IS_SINGLETON_VISITOR =
      new BindingScopingVisitor<Boolean>() {
        @Override
        public Boolean visitNoScoping() {
          return false;
        }

        @Override
        public Boolean visitScopeAnnotation(Class<? extends Annotation> scopeAnnotation) {
          return scopeAnnotation == Singleton.class
              || scopeAnnotation == jakarta.inject.Singleton.class;
        }

        @Override
        public Boolean visitScope(Scope scope) {
          return scope == Scopes.SINGLETON;
        }

        @Override
        public Boolean visitEagerSingleton() {
          return true;
        }
      };

  /**
   * Returns true if {@code binding} is singleton-scoped. If the binding is a {@link
   * com.google.inject.spi.LinkedKeyBinding linked key binding} and belongs to an injector (ie. it
   * was retrieved via {@link Injector#getBinding Injector.getBinding()}), then this method will