54 lines
1.3 KiB
TypeScript
54 lines
1.3 KiB
TypeScript
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import type {VoidFn} from '../types'
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import AbstractDerivation from './AbstractDerivation'
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const noop = () => {}
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export default class DerivationFromSource<V> extends AbstractDerivation<V> {
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private _untapFromChanges: () => void
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private _cachedValue: undefined | V
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private _hasCachedValue: boolean
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constructor(
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private readonly _tapToSource: (listener: (newValue: V) => void) => VoidFn,
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private readonly _getValueFromSource: () => V,
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) {
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super()
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this._untapFromChanges = noop
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this._cachedValue = undefined
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this._hasCachedValue = false
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}
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_recalculate() {
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if (this.isHot) {
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if (!this._hasCachedValue) {
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this._cachedValue = this._getValueFromSource()
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this._hasCachedValue = true
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}
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return this._cachedValue as V
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} else {
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return this._getValueFromSource()
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}
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}
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_keepHot() {
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this._hasCachedValue = false
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this._cachedValue = undefined
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this._untapFromChanges = this._tapToSource((newValue) => {
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this._hasCachedValue = true
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this._cachedValue = newValue
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this._markAsStale(this)
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})
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}
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_becomeCold() {
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this._untapFromChanges()
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this._untapFromChanges = noop
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this._hasCachedValue = false
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this._cachedValue = undefined
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}
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_reactToDependencyBecomingStale() {}
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}
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