Retire DerivationFromSource (1/2)

This is supposed to break the build. In the next commit, I'll implement `HotScope.source()` to fix the build.

packages/dataverse/src/Atom.ts

@@ -1,7 +1,6 @@
 import get from 'lodash-es/get'
 import isPlainObject from 'lodash-es/isPlainObject'
 import last from 'lodash-es/last'
-import DerivationFromSource from './derivations/DerivationFromSource'
 import type {IDerivation} from './derivations/IDerivation'
 import {isDerivation} from './derivations/IDerivation'
 import type {Pointer, PointerType} from './pointer'
@@ -10,6 +9,7 @@ import pointer, {getPointerMeta} from './pointer'
 import type {$FixMe, $IntentionalAny} from './types'
 import type {PathBasedReducer} from './utils/PathBasedReducer'
 import updateDeep from './utils/updateDeep'
+import prism from './derivations/prism/prism'
 
 type Listener = (newVal: unknown) => void
 
@@ -247,10 +247,14 @@ export default class Atom<State extends {}>
    * @param path - The path to create the derivation at.
    */
   getIdentityDerivation(path: Array<string | number>): IDerivation<unknown> {
-    return new DerivationFromSource<$IntentionalAny>(
-      (listener) => this._onPathValueChange(path, listener),
-      () => this.getIn(path),
-    )
+    const subscribe = (listener: (val: unknown) => void) =>
+      this._onPathValueChange(path, listener)
+
+    const getValue = () => this.getIn(path)
+
+    return prism(() => {
+      return prism.source('value', subscribe, getValue)
+    })
   }
 }
 

packages/dataverse/src/Box.ts

@@ -1,5 +1,5 @@
-import DerivationFromSource from './derivations/DerivationFromSource'
 import type {IDerivation} from './derivations/IDerivation'
+import prism from './derivations/prism/prism'
 import Emitter from './utils/Emitter'
 
 /**
@@ -51,10 +51,12 @@ export default class Box<V> implements IBox<V> {
      */
     protected _value: V,
   ) {
-    this._publicDerivation = new DerivationFromSource(
-      (listener) => this._emitter.tappable.tap(listener),
-      this.get.bind(this),
-    )
+    const subscribe = (listener: (val: V) => void) =>
+      this._emitter.tappable.tap(listener)
+    const getValue = () => this._value
+    this._publicDerivation = prism(() => {
+      return prism.source('value', subscribe, getValue)
+    })
   }
 
   /**

packages/dataverse/src/derivations/DerivationFromSource.ts

@@ -1,72 +0,0 @@
-import type {VoidFn} from '../types'
-import AbstractDerivation from './AbstractDerivation'
-
-const noop = () => {}
-
-/**
- * Represents a derivation based on a tappable (subscribable) data source.
- */
-export default class DerivationFromSource<V> extends AbstractDerivation<V> {
-  private _untapFromChanges: () => void
-  private _cachedValue: undefined | V
-  private _hasCachedValue: boolean
-
-  /**
-   * @param _tapToSource - A function that takes a listener and subscribes it to the underlying data source.
-   * @param _getValueFromSource - A function that returns the current value of the data source.
-   */
-  constructor(
-    private readonly _tapToSource: (listener: (newValue: V) => void) => VoidFn,
-    private readonly _getValueFromSource: () => V,
-  ) {
-    super()
-    this._untapFromChanges = noop
-    this._cachedValue = undefined
-    this._hasCachedValue = false
-  }
-
-  /**
-   * @internal
-   */
-  _recalculate() {
-    if (this.isHot) {
-      if (!this._hasCachedValue) {
-        this._cachedValue = this._getValueFromSource()
-        this._hasCachedValue = true
-      }
-      return this._cachedValue as V
-    } else {
-      return this._getValueFromSource()
-    }
-  }
-
-  /**
-   * @internal
-   */
-  _keepHot() {
-    this._hasCachedValue = false
-    this._cachedValue = undefined
-
-    this._untapFromChanges = this._tapToSource((newValue) => {
-      this._hasCachedValue = true
-      this._cachedValue = newValue
-      this._markAsStale(this)
-    })
-  }
-
-  /**
-   * @internal
-   */
-  _becomeCold() {
-    this._untapFromChanges()
-    this._untapFromChanges = noop
-
-    this._hasCachedValue = false
-    this._cachedValue = undefined
-  }
-
-  /**
-   * @internal
-   */
-  _reactToDependencyBecomingStale() {}
-}

packages/dataverse/src/derivations/prism/prism.ts

@@ -28,7 +28,6 @@ class HotHandle<V> {
     this._dependents.delete(d)
   }
   addDependent(d: IDependent) {
-    // having no dependents means the prism is currently cold
     this._dependents.add(d)
   }
   private _didMarkDependentsAsStale: boolean = false
@@ -328,7 +327,7 @@ class PrismDerivation<V> implements IDerivation<V> {
     if (state.hot) {
       val = state.handle.getValue()
     } else {
-      val = ColdStuff.calculateColdPrism(this._fn)
+      val = calculateColdPrism(this._fn)
     }
 
     reportResolutionEnd(this)
@@ -383,6 +382,11 @@ interface PrismScope {
   state<T>(key: string, initialValue: T): [T, (val: T) => void]
   ref<T>(key: string, initialValue: T): IRef<T>
   sub(key: string): PrismScope
+  source<V>(
+    key: string,
+    subscribe: (fn: (val: V) => void) => VoidFn,
+    getValue: () => V,
+  ): V
 }
 
 class HotScope implements PrismScope {
@@ -482,6 +486,12 @@ class HotScope implements PrismScope {
     }
     this.effects.clear()
   }
+
+  source<V>(
+    key: string,
+    subscribe: (fn: (val: V) => void) => VoidFn,
+    getValue: () => V,
+  ): V {}
 }
 
 function cleanupScopeStack(scope: HotScope) {
@@ -694,6 +704,19 @@ const possibleDerivationToValue = <
   }
 }
 
+function source<V>(
+  key: string,
+  subscribe: (fn: (val: V) => void) => VoidFn,
+  getValue: () => V,
+): V {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.source() is called outside of a prism() call.`)
+  }
+
+  return scope.source(key, subscribe, getValue)
+}
+
 type IPrismFn = {
   <T>(fn: () => T): IDerivation<T>
   ref: typeof ref
@@ -704,6 +727,7 @@ type IPrismFn = {
   scope: typeof scope
   sub: typeof sub
   inPrism: typeof inPrism
+  source: typeof source
 }
 
 /**
@@ -736,28 +760,33 @@ class ColdScope implements PrismScope {
   sub(key: string): ColdScope {
     return new ColdScope()
   }
+  source<V>(
+    key: string,
+    subscribe: (fn: (val: V) => void) => VoidFn,
+    getValue: () => V,
+  ): V {
+    return getValue()
+  }
 }
 
-namespace ColdStuff {
-  export function calculateColdPrism<V>(fn: () => V): V {
-    const scope = new ColdScope()
-    hookScopeStack.push(scope)
-    let value: V
-    try {
-      value = fn()
-    } catch (error) {
-      console.error(error)
-    } finally {
-      const topOfTheStack = hookScopeStack.pop()
-      if (topOfTheStack !== scope) {
-        console.warn(
-          // @todo guide the user to report the bug in an issue
-          `The Prism hook stack has slipped. This is a bug.`,
-        )
-      }
+function calculateColdPrism<V>(fn: () => V): V {
+  const scope = new ColdScope()
+  hookScopeStack.push(scope)
+  let value: V
+  try {
+    value = fn()
+  } catch (error) {
+    console.error(error)
+  } finally {
+    const topOfTheStack = hookScopeStack.pop()
+    if (topOfTheStack !== scope) {
+      console.warn(
+        // @todo guide the user to report the bug in an issue
+        `The Prism hook stack has slipped. This is a bug.`,
+      )
     }
-    return value!
   }
+  return value!
 }
 
 prism.ref = ref
@@ -768,5 +797,6 @@ prism.state = state
 prism.scope = scope
 prism.sub = sub
 prism.inPrism = inPrism
+prism.source = source
 
 export default prism

packages/dataverse/src/index.ts

@@ -9,7 +9,6 @@ export {default as Atom, val, valueDerivation} from './Atom'
 export {default as Box} from './Box'
 export type {IBox} from './Box'
 export {default as AbstractDerivation} from './derivations/AbstractDerivation'
-export {default as DerivationFromSource} from './derivations/DerivationFromSource'
 export {isDerivation} from './derivations/IDerivation'
 export type {IDerivation} from './derivations/IDerivation'
 export {default as iterateAndCountTicks} from './derivations/iterateAndCountTicks'