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feat(useDataEngine): make engine instance a referential constant #934

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feat(useDataEngine): make engine instance a referential constant #934

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20 changes: 20 additions & 0 deletions services/data/src/react/hooks/useDataEngine.test.tsx
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
import { renderHook } from '@testing-library/react-hooks'
import * as React from 'react'
import { CustomDataProvider } from '../components/CustomDataProvider'
import { useDataEngine } from './useDataEngine'

describe('useDataEngine', () => {
it('should preserve the referential identity of the engine', () => {
const wrapper = ({ children }) => (
<CustomDataProvider data={{}}>{children}</CustomDataProvider>
)

const { result, rerender } = renderHook(useDataEngine, { wrapper })
const { current: firstEngineResult } = result

rerender()
const { current: secondEngineResult } = result

expect(firstEngineResult).toBe(secondEngineResult)
})
})
14 changes: 10 additions & 4 deletions services/data/src/react/hooks/useDataEngine.ts
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Original file line number Diff line number Diff line change
@@ -1,8 +1,14 @@
import { useContext } from 'react'
import { useContext, useState } from 'react'
import { DataEngine } from '../../engine'
import { DataContext } from '../context/DataContext'

export const useDataEngine = () => {
const context = useContext(DataContext)
function useConst<T>(initializer: () => T): T {
const [value] = useState(initializer)
return value
}
Comment on lines +5 to +8
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Suggested change
function useConst<T>(initializer: () => T): T {
const [value] = useState(initializer)
return value
}
function useInstanceVariable<T>(initializer: () => T, dependencies: any[]): T {
const [value, setValue] = useState(initializer)
const initializedRef = useRef(false)
useEffect(() => {
if (!initializedRef.current) {
initializedRef.current = true
return
}
setValue(initializer())
}, dependencies)
return value
}

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Maybe something like this instead, to support updates when deps change?

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Note however that this will cause double-renders on dependency updates...

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useInstanceVariable would be used in DataProvider and CustomDataProvider instead of in useDataEngine right?

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Sounds a lot like we could just use useMemo instead of useConst?

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@Mohammer5 this is super old... but no, there's a difference because useConst guarantees referential integrity while useMemo might re-initialize in certain situations since it is only considered a performance optimization.

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@Mohammer5 Mohammer5 Dec 16, 2021 •
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Yeah, I also figured out the other day that useMemo does not guarantee that..
I think for simplicity's sake, the following might be the most pragmatic with the least amount of abstractions:

function useDataEngine = (): DataEngine => {
    const context = useContext(DataContext)
    const [instance, setInstance] = useState(context.engine)
    
   useEffect(() => {
        setInstance(context.engine)
    }, [context.engine])

    return value
}


return context.engine
export const useDataEngine = (): DataEngine => {
const context = useContext(DataContext)
const engine = useConst<DataEngine>(() => context.engine)
return engine
}