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updateIn doesn't properly handle notSetValue #113

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Methuselah96 opened this issue Oct 17, 2020 · 4 comments
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updateIn doesn't properly handle notSetValue #113

Methuselah96 opened this issue Oct 17, 2020 · 4 comments
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@Methuselah96
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From @migueloller on Fri, 30 Nov 2018 21:50:42 GMT

What happened

updateIn doesn't properly handle notSetValue.

How to reproduce

const { updateIn } = require('immutable')
const original = { x: { y: { z: 123 } } }
const NOT_SET = { NOT_SET: true }
console.log(updateIn(original, ['x', 'y'], NOT_SET, val => NOT_SET)) // { x: { y: { NOT_SET: true } } }

Expected the log output to be { x: {} } instead. Is this intended behavior?

Copied from original issue: immutable-js#1657
@Methuselah96
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Correct behavior.

@migueloller
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@Methuselah96, how is this correct behavior? If the updater returns the "not set" value, then the value at that key should be unset (i.e., removed).

@migueloller
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For any future readers, explanation is here: immutable-js#1657 (comment)

@migueloller
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migueloller commented Nov 21, 2020 •
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Based on the implementation, it seems that notSetValue is returned back to the updateIn caller if the value itself is not set. So it seems that it is not just limited to the value passed to the updater function if there is no value at the key path.

immutable-js/src/functional/updateIn.js

Line 31 in 7a79603

return updatedValue === NOT_SET ? notSetValue : updatedValue;

I also do see, though, how notSetValue is indeed passed to the updater, and that makes sense:

immutable-js/src/functional/updateIn.js

Lines 44 to 45 in 7a79603

const existingValue = wasNotSet ? notSetValue : existing;
const newValue = updater(existingValue);

I was just expecting setting something to notSetValue would be equivalent to "unsetting" it.

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