92 lines
2.5 KiB
TypeScript
92 lines
2.5 KiB
TypeScript
import type Ticker from '../Ticker'
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import type {$IntentionalAny, VoidFn} from '../types'
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type IDependent = (msgComingFrom: IDerivation<$IntentionalAny>) => void
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/**
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* Common interface for derivations.
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*/
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export interface IDerivation<V> {
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/**
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* Whether the object is a derivation.
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*/
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isDerivation: true
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/**
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* Whether the derivation is hot.
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*/
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isHot: boolean
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/**
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* Calls `listener` with a fresh value every time the prism _has_ a new value, throttled by Ticker.
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*/
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onChange(
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ticker: Ticker,
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listener: (v: V) => void,
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immediate?: boolean,
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): VoidFn
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onStale(cb: () => void): VoidFn
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/**
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* Keep the derivation hot, even if there are no tappers (subscribers).
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*/
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keepHot(): VoidFn
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/**
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* Add a derivation as a dependent of this derivation.
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*
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* @param d - The derivation to be made a dependent of this derivation.
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*
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* @see removeDependent
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*/
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addDependent(d: IDependent): void
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/**
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* Remove a derivation as a dependent of this derivation.
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*
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* @param d - The derivation to be removed from as a dependent of this derivation.
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*
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* @see addDependent
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*/
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removeDependent(d: IDependent): void
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/**
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* Gets the current value of the derivation. If the value is stale, it causes the derivation to freshen.
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*/
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getValue(): V
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/**
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* Creates a new derivation from this derivation using the provided mapping function. The new derivation's value will be
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* `fn(thisDerivation.getValue())`.
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*
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* @param fn - The mapping function to use. Note: it accepts a plain value, not a derivation.
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*/
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map<T>(fn: (v: V) => T): IDerivation<T>
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/**
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* Same as {@link IDerivation.map}, but the mapping function can also return a derivation, in which case the derivation returned
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* by `flatMap` takes the value of that derivation.
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*
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* @example
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* ```ts
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* // Simply using map() here would return the inner derivation when we call getValue()
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* new Box(3).derivation.map((value) => new Box(value).derivation).getValue()
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*
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* // Using flatMap() eliminates the inner derivation
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* new Box(3).derivation.flatMap((value) => new Box(value).derivation).getValue()
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* ```
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*
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* @param fn - The mapping function to use. Note: it accepts a plain value, not a derivation.
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*/
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flatMap<R>(
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fn: (v: V) => R,
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): IDerivation<R extends IDerivation<infer T> ? T : R>
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}
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/**
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* Returns whether `d` is a derivation.
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*/
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export function isDerivation(d: any): d is IDerivation<unknown> {
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return d && d.isDerivation && d.isDerivation === true
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}
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