A util method to add computed to state

[thelinuxlich]

Right now it's natural to add a reactive property to a proxified state object, what's missing is a util method for doing the same with computed:

import { addComputed } from 'valtio/utils'
import state from './store/root' 

addComputed(state, { double(snap) { return snap.counter * 2 } })

[dai-shi]

Hey, this is interesting. Can we drop proxyWithComputed if we support chaining addComputed?

[dai-shi]

Maybe not. I don’t have an idea yet to support nested computeds with addComputed.

[thelinuxlich]

If it's possible to add multiple computeds in a single call, I'd say yes

[dai-shi]

OK, I might need to change a signature significantly. It's more for #85. Let's see how you like it.

[dai-shi]

Hmm, my challenges are not very successful.

https://github.com/pmndrs/valtio/tree/feat/add-computed
The result doesn't seem to be very handy as it still requires proxyWithComputed.

https://github.com/pmndrs/valtio/tree/feat/add-computed-2
This one can't support computed setters.

In either case, nested computed is tricky with typescript.

Is there a real use case to add computed afterward?

[thelinuxlich]

@dai-shi IMO the first branch accomplishes the feature, although not as you'd like (deprecating proxyWithComputed)

Real use cases:

• Augmenting a state tree with reactive/computed fields through plugins(or mixins)
• Dynamic reactive/computed field generation(through a CMS, smart form generator, etc)