Idea: introduce abstraction for computeds with arguments

[mweststrate]

See mobxjs/mobx#1388 (comment) and mobxjs/mobx#1388 (comment). This could potentially replace createTransformer as well.

Signature:
memoizedComputed<T>(expression: T, invalidationStrategy?: "auto" | "never" | number = "auto"): T

strategies:

• "auto": remove entries from the memoization table as soon as they become unobserved
• "never": we don't care, cache forever (that is, until the computeds and all things they depend on are GC-ed)
• number: remove entries after they have not been hit a the specified amount of time. Probably not needed in a first versoin.

Example:

class Todos {
  @observable todos = []
  
  private todosByUserCache = new Map()

  getAllTodosByUser = memoizedComputed((userId) => {
    if (this.todosByUserCache.has(userId))
      return this.todosByUserCache.get(userId).get()
      
    const computedFilter = computed(() => this.todos.filter(todo => todo.user === userId))
    this.todosByUserCache.set(userId, computedFilter)
    return todosByUserCache.get()
  })
}

const todos = new Todos()
const myTodos: Todo[] = todos.getAllTodosByUser("17")

[bourquep]

Woah, it's funny how you opened this issue 5 hours ago and my coworker and I were trying to figure out how we'd solve this very issue 10 hours ago 🤓

[urugator]

Does "never" pass keepAlive: true to the underlying computed ? I think it would make sense? Then maybe computed API could be preserved (without number support)... and perhaps the user should be able to provide other options like equals...?

[mweststrate]

Good point, yes I think so. Didn't think it that far through :)

…

On Fri, Mar 22, 2019 at 9:25 AM urugator ***@***.***> wrote: Does "never" pass keepAlive: true to the underlying computed ? I think it would make sense? Then maybe computed API could be preserved (without number support)... and perhaps the user should be able to provide other options like equals...? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#184 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABvGhGYmmc7t9wTI-mLBGqLblzXUIz7Hks5vZJOFgaJpZM4bzk8I> .

[dreamair]

For one-object-argument functions (a User object instead of just the userId in your example) a WeakMap could help automatically cleaning up entries with the argument-object being GCed. It would be like an "extension" to the User indirectly holding a computed member for all his todos without depending on them.
I don't see this working for multiple arguments or primitives though.

[mweststrate]

Released as 5.4.0!