upsert

[char0n]

Is your feature request related to a problem? Please describe.

Polymorphic updating or inserting in one operation. We're using ad hoc polymorphism here.

Describe the solution you'd like

// working on objects
upsert('key', () => 'new value', () => 'initial value', {}); // {key: 'initial value'}
upsert('key', () => 'new value', () => 'initial value', {key: 'value'}); // {key: 'new value'}

// working on arrays
upsert(1, () => 'new value', () => 'initial value', []); // sparse array of [, 'initial value']
upsert(1, () => 'new value', () => 'initial value', ['first value', 'second vaue']); // ['first value', 'new value']

// working on maps
upsert('key', () => 'new value', () => 'initial value', new Map()); // Map({key: 'initial value'})
upsert('key', () => 'new value', () => 'initial value', new Map([['key', 'new value']])); // Map({key: 'new value'})

Describe alternatives you've considered

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Additional context

TC39 Map.upsert proposal: https://github.com/tc39/proposal-upsert (stage 2 proposal). Our version of polymorhic upsert can work on multiple JavaScript types.

[char0n]

We discussed the viability of this function with TC39 proposal author and he agrees the function make sense if the library (R, RA) already support polymorphic functions.