src/vs/base/common/observableInternal/experimental/reducer.ts

88 LOC · 80 covered · 8 uncovered · 6 ranges · 47 concepts · 2 introducers · 42 tests

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  /*---------------------------------------------------------------------------------------------
  
reducer.ts ×3

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   *  Copyright (c) Microsoft Corporation. All rights reserved.
  
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   *  Licensed under the MIT License. See License.txt in the project root for license information.
  
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   *--------------------------------------------------------------------------------------------*/
  
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  import { EqualityComparer, strictEquals, BugIndicatingError } from '../commonFacade/deps.js';
  
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  import { IObservable, IObservableWithChange, ISettableObservable } from '../base.js';
  
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  import { subtransaction } from '../transaction.js';
  
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  import { IChangeTracker } from '../changeTracker.js';
  
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  import { DebugNameData, DebugOwner } from '../debugName.js';
  
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  import { DerivedWithSetter, IDerivedReader } from '../observables/derivedImpl.js';
  
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  import { DebugLocation } from '../debugLocation.js';
  
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  export interface IReducerOptions<T, TChangeSummary = void, TOutChange = void> {
  
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  	/**
  
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  	 * Is called to create the initial value of the observable when it becomes observed.
  
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  	*/
  
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  	initial: T | (() => T);
  
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  	/**
  
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  	 * Is called to dispose the observable value when it is no longer observed.
  
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  	*/
  
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  	disposeFinal?(value: T): void;
  
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  	changeTracker?: IChangeTracker<TChangeSummary>;
  
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  	equalityComparer?: EqualityComparer<T>;
  
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  	/**
  
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  	 * Applies the changes to the value.
  
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  	 * Use `reader.reportChange` to report change details or to report a change if the same value is returned.
  
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  	*/
  
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  	update(reader: IDerivedReader<TOutChange>, previousValue: T, changes: TChangeSummary): T;
  
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  }
  
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  /**
  
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   * Creates an observable value that is based on values and changes from other observables.
  
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   * Additionally, a reducer can report how that state changed.
  
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  */
  
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  export function observableReducer<T, TInChanges, TOutChange = void>(owner: DebugOwner, options: IReducerOptions<T, TInChanges, TOutChange>): SimplifyObservableWithChange<T, TOutChange> {
  
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  	// eslint-disable-next-line local/code-no-any-casts
  
reducer.ts ×3

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  	return observableReducerSettable<T, TInChanges, TOutChange>(owner, options) as any;
  
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  }
  
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reducer.ts ×3

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  /**
  
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   * Creates an observable value that is based on values and changes from other observables.
  
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   * Additionally, a reducer can report how that state changed.
  
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  */
  
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  export function observableReducerSettable<T, TInChanges, TOutChange = void>(owner: DebugOwner, options: IReducerOptions<T, TInChanges, TOutChange>): ISettableObservable<T, TOutChange> {
  
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  	let prevValue: T | undefined = undefined;
  
reducer.ts ×3

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  	let hasValue = false;
  
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  	const d = new DerivedWithSetter(
  
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  		new DebugNameData(owner, undefined, options.update),
  
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  		(reader: IDerivedReader<TOutChange>, changeSummary) => {
  
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  			if (!hasValue) {
  
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  				prevValue = options.initial instanceof Function ? options.initial() : options.initial;
  
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  				hasValue = true;
  
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  			}
  
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  			const newValue = options.update(reader, prevValue!, changeSummary);
  
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  			prevValue = newValue;
  
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  			return newValue;
  
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  		},
  
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  		options.changeTracker,
  
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  		() => {
  
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  			if (hasValue) {
  
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  				options.disposeFinal?.(prevValue!);
  
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  				hasValue = false;
  
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  			}
  
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  		},
  
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  		options.equalityComparer ?? strictEquals,
  
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  		(value, tx, change) => {
  
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  			if (!hasValue) {
  
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  				throw new BugIndicatingError('Can only set when there is a listener! This is to prevent leaks.');
  
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  			}
  
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  			subtransaction(tx, tx => {
  
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  				prevValue = value;
  
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  				d.setValue(value, tx, change);
  
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  			});
  
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  		},
  
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  		DebugLocation.ofCaller()
  
reducer.ts ×3

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  	);
  
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  	return d;
  
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  }
  
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reducer.ts ×3

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  /**
  
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   * Returns IObservable<T> if TChange is void, otherwise IObservableWithChange<T, TChange>
  
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  */
  
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  type SimplifyObservableWithChange<T, TChange> = TChange extends void ? IObservable<T> : IObservableWithChange<T, TChange>;