src/vs/base/common/observableInternal/experimental/utils.ts
60 LOC · 26 covered · 34 uncovered · 2 ranges · 6771 concepts · 1 introducers · 3467 tests
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/*---------------------------------------------------------------------------------------------
devToolsLogger.ts ×24
* Copyright (c) Microsoft Corporation. All rights reserved.
* Licensed under the MIT License. See License.txt in the project root for license information.
*--------------------------------------------------------------------------------------------*/
import { IObservable, IReader } from '../base.js';
import { BugIndicatingError, DisposableStore } from '../commonFacade/deps.js';
import { DebugOwner, getDebugName, DebugNameData } from '../debugName.js';
import { observableFromEvent } from '../observables/observableFromEvent.js';
import { autorunOpts } from '../reactions/autorun.js';
import { derivedObservableWithCache } from '../utils/utils.js';
/**
* Creates an observable that has the latest changed value of the given observables.
* Initially (and when not observed), it has the value of the last observable.
* When observed and any of the observables change, it has the value of the last changed observable.
* If multiple observables change in the same transaction, the last observable wins.
*/
export function latestChangedValue<T extends IObservable<any>[]>(owner: DebugOwner, observables: T): IObservable<ReturnType<T[number]['get']>> {
if (observables.length === 0) {
throw new BugIndicatingError();
}
let hasLastChangedValue = false;
let lastChangedValue: unknown = undefined;
const result = observableFromEvent<any, void>(owner, cb => {
const store = new DisposableStore();
for (const o of observables) {
store.add(autorunOpts({ debugName: () => getDebugName(result, new DebugNameData(owner, undefined, undefined)) + '.updateLastChangedValue' }, reader => {
hasLastChangedValue = true;
lastChangedValue = o.read(reader);
cb();
}));
}
store.add({
dispose() {
hasLastChangedValue = false;
lastChangedValue = undefined;
},
});
return store;
}, () => {
if (hasLastChangedValue) {
return lastChangedValue;
} else {
return observables[observables.length - 1].get();
}
});
return result;
}
/**
* Works like a derived.
* However, if the value is not undefined, it is cached and will not be recomputed anymore.
* In that case, the derived will unsubscribe from its dependencies.
*/
export function derivedConstOnceDefined<T>(owner: DebugOwner, fn: (reader: IReader) => T): IObservable<T | undefined> {
return derivedObservableWithCache<T | undefined>(owner, (reader, lastValue) => lastValue ?? fn(reader));
}