Batching support

[pirelenito]

The main motivation is to prevent execution of effects with "transient" values. The pseudo-code below explains in a better way a very common scenario when working with Facets:

type User = { name: string; login: string }

// Starting with a single Facet
const [user, setUser] = useFacetState<User>({ name: 'Initial Name', login: 'Initial Login' })

// We might map it into more specific properties
const nameFacet = useFacetMap(({ name }) => name, [], [user])
const loginFacet = useFacetMap(({ login }) => login, [], [user])

// But latter, we could have an effect that depends on both values
useFacetEffect(
  (name, login) => {
    // Before batching, this effect would be called twice
    // - First time: with name containing the new value, but login with old
    // - Second time : with both name and login containing their new values
  },
  [],
  [nameFacet, loginFacet],
)

Batching by default

It changes the default implementation of createFacet to automatically start a batch when its updated, so consumers will get the benefit of batching without having to update any of their code.

Batching multiple Facets

In addition, it does introduce a new API batch, that allows batching together multiple Facet updates.

batch(() => {
  facetA.set('new value')
  facetB.set('something else')
})

This API was inspired by existing community patterns, such as Solid's batch.

Performance

Benchmarks done in the internal Mojang codebase showed either an improvement or similar performance after this change (backed by the benchmarks in this repository).

Release candidates

To try this out, we've been publishing RCs at batch...batch-rc

[xaviervia]

Let's remain consistent and export with *. I know there are other two functions being exported and maybe they were meant as internal, but I think there's value in exposing them, we don't yet know if there is no use for them in third party library code.

[pirelenito]

Exactly, the reason was to keep them private.

The main risk with open-source packages is that once an API is public and used... its a wider surface we need to keep compatible.