46 lines
1.2 KiB
TypeScript
46 lines
1.2 KiB
TypeScript
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import Emitter from '../utils/Emitter'
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import type {default as Tappable} from '../utils/Tappable'
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import type {IDerivation} from './IDerivation'
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/**
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* Just like DerivationEmitter, except it doesn't emit the value and doesn't need a ticker
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*/
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export default class DerivationValuelessEmitter<V> {
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_derivation: IDerivation<V>
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_emitter: Emitter<void>
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_hadTappers: boolean
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constructor(
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derivation: IDerivation<V>,
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readonly dontEmitValues: boolean = false,
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) {
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this._derivation = derivation
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this._emitter = new Emitter()
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this._emitter.onNumberOfTappersChange(() => {
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this._reactToNumberOfTappersChange()
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})
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this._hadTappers = false
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return this
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}
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private _possiblyMarkAsStale = () => {
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this._emitter.emit(undefined)
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}
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_reactToNumberOfTappersChange() {
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const hasTappers = this._emitter.hasTappers()
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if (hasTappers !== this._hadTappers) {
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this._hadTappers = hasTappers
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if (hasTappers) {
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this._derivation.addDependent(this._possiblyMarkAsStale)
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} else {
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this._derivation.removeDependent(this._possiblyMarkAsStale)
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}
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}
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}
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tappable(): Tappable<void> {
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return this._emitter.tappable
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}
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}
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