refactor(Subscription): minor size reduction (#5707)

- Reduces the size of `Subscription` slightly.
- Moves back to a single property for single parent, many parents, scenarios
- Updates the type of `Teardown` to not be so loose. `Function` shouldn't be used.

api_guard/dist/types/index.d.ts

@@ -581,7 +581,7 @@ export interface SubscriptionLike extends Unsubscribable {
 
 export declare type Tail<X extends any[]> = ((...args: X) => any) extends ((arg: any, ...rest: infer U) => any) ? U : never;
 
-export declare type TeardownLogic = Subscription | Unsubscribable | Function | void;
+export declare type TeardownLogic = Subscription | Unsubscribable | (() => void) | void;
 
 export declare function throwError(errorFactory: () => any): Observable<never>;
 export declare function throwError(error: any): Observable<never>;

src/internal/Subscription.ts

@@ -1,7 +1,7 @@
 /** @prettier */
 import { isFunction } from './util/isFunction';
 import { UnsubscriptionError } from './util/UnsubscriptionError';
-import { SubscriptionLike, TeardownLogic } from './types';
+import { SubscriptionLike, TeardownLogic, Unsubscribable } from './types';
 
 /**
  * Represents a disposable resource, such as the execution of an Observable. A
@@ -27,11 +27,7 @@ export class Subscription implements SubscriptionLike {
  */
  public closed = false;
 
- /** If this subscription has been added to one parent, it will show up here */
- private _singleParent: Subscription | null = null;
-
- /** If this subscription has been added to more than one parent, they will show up here. */
- private _parents: Subscription[] | null = null;
+ private _parentage: Subscription[] | Subscription | null = null;
 
  /**
  * The list of registered teardowns to execute upon unsubscription. Adding and removing from this
@@ -58,17 +54,13 @@ export class Subscription implements SubscriptionLike {
  this.closed = true;
 
  // Remove this from it's parents.
-
- const { _singleParent } = this;
- let _parents: Subscription[] | null;
- if (_singleParent) {
- this._singleParent = null;
- _singleParent.remove(this);
- } else if ((_parents = this._parents)) {
- this._parents = null;
- for (const parent of _parents) {
+ const { _parentage } = this;
+ if (Array.isArray(_parentage)) {
+ for (const parent of _parentage) {
  parent.remove(this);
  }
+ } else {
+ _parentage?.remove(this);
  }
 
  const { initialTeardown } = this;
@@ -81,15 +73,11 @@ export class Subscription implements SubscriptionLike {
  }
 
  const { _teardowns } = this;
- this._teardowns = null;
  if (_teardowns) {
+ this._teardowns = null;
  for (const teardown of _teardowns) {
  try {
- if (typeof teardown === 'function') {
- teardown();
- } else {
- teardown.unsubscribe();
- }
+ execTeardown(teardown);
  } catch (err) {
  errors = errors ?? [];
  if (err instanceof UnsubscriptionError) {
@@ -132,11 +120,7 @@ export class Subscription implements SubscriptionLike {
  if (this.closed) {
  // If this subscription is already closed,
  // execute whatever teardown is handed to it automatically.
- if (typeof teardown === 'function') {
- teardown();
- } else {
- teardown.unsubscribe();
- }
+ execTeardown(teardown);
  } else {
  if (teardown instanceof Subscription) {
  // We don't add closed subscriptions, and we don't add the same subscription
@@ -146,8 +130,7 @@ export class Subscription implements SubscriptionLike {
  }
  teardown._addParent(this);
  }
- this._teardowns = this._teardowns ?? [];
- this._teardowns.push(teardown);
+ (this._teardowns = this._teardowns ?? []).push(teardown);
  }
  }
  }
@@ -158,7 +141,8 @@ export class Subscription implements SubscriptionLike {
  * @param parent the parent to check for
  */
  private _hasParent(parent: Subscription) {
- return this._singleParent === parent || this._parents?.includes(parent) || false;
+ const { _parentage } = this;
+ return _parentage === parent || (Array.isArray(_parentage) && _parentage.includes(parent));
  }
 
  /**
@@ -169,37 +153,22 @@ export class Subscription implements SubscriptionLike {
  * @param parent The parent subscription to add
  */
  private _addParent(parent: Subscription) {
- const { _singleParent } = this;
- let _parents: Subscription[] | null;
- if (_singleParent) {
- // We already have one parent so we'll need to expand
- // to use an array
- this._parents = [_singleParent, parent];
- this._singleParent = null;
- } else if ((_parents = this._parents)) {
- // We already have more than one parent, so just add on to that array.
- _parents.push(parent);
- } else {
- // This is our first parent.
- this._singleParent = parent;
- }
+ const { _parentage } = this;
+ this._parentage = Array.isArray(_parentage) ? (_parentage.push(parent), _parentage) : _parentage ? [_parentage, parent] : parent;
  }
 
  /**
  * Called on a child when it is removed via {@link remove}.
  * @param parent The parent to remove
  */
  private _removeParent(parent: Subscription) {
- const { _singleParent } = this;
- let _parents: Subscription[] | null;
- if (_singleParent) {
- if (_singleParent === parent) {
- this._singleParent = null;
- }
- } else if ((_parents = this._parents)) {
- const index = _parents.indexOf(parent);
- if (index >= 0) {
- _parents.splice(index, 1);
+ const { _parentage } = this;
+ if (_parentage === parent) {
+ this._parentage = null;
+ } else if (Array.isArray(_parentage)) {
+ const index = _parentage.indexOf(parent);
+ if (0 <= index) {
+ _parentage.splice(index, 1);
  }
  }
  }
@@ -243,3 +212,11 @@ export function isSubscription(value: any): value is Subscription {
  typeof value.unsubscribe === 'function')
  );
 }
+
+function execTeardown(teardown: Unsubscribable | (() => void)) {
+ if (typeof teardown === 'function') {
+ teardown();
+ } else {
+ teardown.unsubscribe();
+ }
+}

src/internal/types.ts

@@ -51,7 +51,7 @@ export interface Unsubscribable {
  unsubscribe(): void;
 }
 
-export type TeardownLogic = Subscription | Unsubscribable | Function | void;
+export type TeardownLogic = Subscription | Unsubscribable | (() => void) | void;
 
 export interface SubscriptionLike extends Unsubscribable {
  unsubscribe(): void;