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feat(core): experimental resource() API for async dependencies (#58255)
Implement a new experimental API, called `resource()`. Resources are asynchronous dependencies that are managed and delivered through the signal graph. Resources are defined by their reactive request function and their asynchronous loader, which retrieves the value of the resource for a given request value. For example, a "current user" resource may retrieve data for the current user, where the request function derives the API call to make from a signal of the current user id. Resources are represented by the `Resource<T>` type, which includes signals for the resource's current value as well as its state. `WritableResource<T>` extends that type to allow for local mutations of the resource through its `value` signal (which is therefore two-way bindable). PR Close #58255
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‎goldens/public-api/core/index.api.md‎

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// @public
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export function resolveForwardRef<T>(type: T): T;
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// @public
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export interface Resource<T> {
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readonly error: Signal<unknown>;
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hasValue(): this is Resource<T> & {
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value: Signal<T>;
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};
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readonly isLoading: Signal<boolean>;
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reload(): boolean;
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readonly status: Signal<ResourceStatus>;
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readonly value: Signal<T | undefined>;
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}
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// @public
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export function resource<T, R>(options: ResourceOptions<T, R>): ResourceRef<T>;
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// @public
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export type ResourceLoader<T, R> = (param: ResourceLoaderParams<R>) => PromiseLike<T>;
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// @public
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export interface ResourceLoaderParams<R> {
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// (undocumented)
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abortSignal: AbortSignal;
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// (undocumented)
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previous: {
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status: ResourceStatus;
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};
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// (undocumented)
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request: Exclude<NoInfer<R>, undefined>;
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}
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// @public
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export interface ResourceOptions<T, R> {
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equal?: ValueEqualityFn<T>;
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injector?: Injector;
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loader: ResourceLoader<T, R>;
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request?: () => R;
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}
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// @public
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export interface ResourceRef<T> extends WritableResource<T> {
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destroy(): void;
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}
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// @public
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export enum ResourceStatus {
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Error = 1,
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Idle = 0,
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Loading = 2,
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Local = 5,
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Reloading = 3,
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Resolved = 4
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}
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// @public
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export function runInInjectionContext<ReturnT>(injector: Injector, fn: () => ReturnT): ReturnT;
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abstract onDestroy(callback: Function): void;
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}
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// @public
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export interface WritableResource<T> extends Resource<T> {
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// (undocumented)
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asReadonly(): Resource<T>;
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// (undocumented)
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hasValue(): this is WritableResource<T> & {
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value: WritableSignal<T>;
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};
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set(value: T | undefined): void;
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update(updater: (value: T | undefined) => T | undefined): void;
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// (undocumented)
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readonly value: WritableSignal<T | undefined>;
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}
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// @public
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export interface WritableSignal<T> extends Signal<T> {
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// (undocumented)

‎packages/core/src/core.ts‎

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@@ -89,6 +89,7 @@ export {ErrorHandler} from './error_handler';
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export * from './core_private_export';
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export * from './core_render3_private_export';
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export * from './core_reactivity_export';
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export * from './resource';
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export {SecurityContext} from './sanitization/security';
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export {Sanitizer} from './sanitization/sanitizer';
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export {

‎packages/core/src/resource/api.ts‎

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/**
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* @license
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* Copyright Google LLC All Rights Reserved.
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*
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* Use of this source code is governed by an MIT-style license that can be
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* found in the LICENSE file at https://angular.dev/license
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*/
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import {Injector} from '../di/injector';
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import {Signal, ValueEqualityFn} from '../render3/reactivity/api';
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import {WritableSignal} from '../render3/reactivity/signal';
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/**
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* Status of a `Resource`.
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*
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* @experimental
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*/
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export enum ResourceStatus {
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/**
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* The resource has no valid request and will not perform any loading.
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*
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* `value()` will be `undefined`.
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*/
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Idle,
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/**
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* Loading failed with an error.
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*
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* `value()` will be `undefined`.
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*/
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Error,
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/**
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* The resource is currently loading a new value as a result of a change in its `request`.
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*
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* `value()` will be `undefined`.
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*/
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Loading,
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/**
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* The resource is currently reloading a fresh value for the same request.
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*
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* `value()` will continue to return the previously fetched value during the reloading operation.
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*/
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Reloading,
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/**
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* Loading has completed and the resource has the value returned from the loader.
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*/
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Resolved,
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/**
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* The resource's value was set locally via `.set()` or `.update()`.
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*/
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Local,
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}
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/**
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* A Resource is an asynchronous dependency (for example, the results of an API call) that is
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* managed and delivered through signals.
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*
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* The usual way of creating a `Resource` is through the `resource` function, but various other APIs
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* may present `Resource` instances to describe their own concepts.
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*
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* @experimental
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*/
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export interface Resource<T> {
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/**
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* The current value of the `Resource`, or `undefined` if there is no current value.
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*/
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readonly value: Signal<T | undefined>;
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/**
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* The current status of the `Resource`, which describes what the resource is currently doing and
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* what can be expected of its `value`.
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*/
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readonly status: Signal<ResourceStatus>;
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/**
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* When in the `error` state, this returns the last known error from the `Resource`.
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*/
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readonly error: Signal<unknown>;
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/**
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* Whether this resource is loading a new value (or reloading the existing one).
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*/
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readonly isLoading: Signal<boolean>;
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/**
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* Whether this resource has a valid current value.
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*
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* This function is reactive.
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*/
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hasValue(): this is Resource<T> & {value: Signal<T>};
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/**
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* Instructs the resource to re-load any asynchronous dependency it may have.
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*
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* Note that the resource will not enter its reloading state until the actual backend request is
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* made.
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*
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* @returns true if a reload was initiated, false if a reload was unnecessary or unsupported
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*/
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reload(): boolean;
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}
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/**
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* A `Resource` with a mutable value.
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*
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* Overwriting the value of a resource sets it to the 'local' state.
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*
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* @experimental
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*/
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export interface WritableResource<T> extends Resource<T> {
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readonly value: WritableSignal<T | undefined>;
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hasValue(): this is WritableResource<T> & {value: WritableSignal<T>};
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/**
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* Convenience wrapper for `value.set`.
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*/
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set(value: T | undefined): void;
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/**
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* Convenience wrapper for `value.update`.
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*/
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update(updater: (value: T | undefined) => T | undefined): void;
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asReadonly(): Resource<T>;
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}
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/**
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* A `WritableResource` created through the `resource` function.
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*
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* @experimental
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*/
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export interface ResourceRef<T> extends WritableResource<T> {
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/**
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* Manually destroy the resource, which cancels pending requests and returns it to `idle` state.
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*/
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destroy(): void;
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}
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/**
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* Parameter to a `ResourceLoader` which gives the request and other options for the current loading
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* operation.
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*
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* @experimental
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*/
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export interface ResourceLoaderParams<R> {
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request: Exclude<NoInfer<R>, undefined>;
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abortSignal: AbortSignal;
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previous: {
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status: ResourceStatus;
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};
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}
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/**
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* Loading function for a `Resource`.
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*
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* @experimental
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*/
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export type ResourceLoader<T, R> = (param: ResourceLoaderParams<R>) => PromiseLike<T>;
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/**
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* Options to the `resource` function, for creating a resource.
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*
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* @experimental
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*/
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export interface ResourceOptions<T, R> {
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/**
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* A reactive function which determines the request to be made. Whenever the request changes, the
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* loader will be triggered to fetch a new value for the resource.
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*
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* If a request function isn't provided, the loader won't rerun unless the resource is reloaded.
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*/
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request?: () => R;
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/**
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* Loading function which returns a `Promise` of the resource's value for a given request.
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*/
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loader: ResourceLoader<T, R>;
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/**
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* Equality function used to compare the return value of the loader.
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*/
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equal?: ValueEqualityFn<T>;
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/**
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* Overrides the `Injector` used by `resource`.
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*/
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injector?: Injector;
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}

‎packages/core/src/resource/index.ts‎

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/**
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* @license
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* Copyright Google LLC All Rights Reserved.
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*
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* Use of this source code is governed by an MIT-style license that can be
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* found in the LICENSE file at https://angular.dev/license
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*/
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export * from './api';
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export {resource} from './resource';

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