Mobx: Remove inferring argumentless functions to computed properties in `observable`

[mweststrate]

See #421. Breaking change so for next major

For migration purposes MobX should warn in a next minor if an function is passed without marking it either with asReference, computed or get

[mattruby]

So this change will mark the beginning of 3.0.0?

On Sep 1, 2016 4:21 PM, "Michel Weststrate" [email protected]
wrote:

See #421 https://github.com/mobxjs/mobx/issues/421. Breaking change so
for next major

For migration purposes MobX should warn in a next minor if an function is
passed without marking it either with asReference, computed or get

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[hccampos]

Sounds like a welcome change. In my case it shouldn't even break anything. I usually only pass pure data into observable and extendObservable and let the decorators take care of computed, observable and action.

[andykog]

@mweststrate, just to make it clear, we replacing syntax like this:

observable({
   x: () => this.y
});

with equal alternative:

observable({
   x: computed(() => this.y)
});

right?

[mweststrate]

Both are still supported, first will be deprecated by this story, idiomatic will be:

observable({
   get x() { return this.y }
});

Biggest advantage is that it avoids subtle errors with this (your example for example would have an undefined this)

[andykog]

@mweststrate, basically, ability to define getter in current context may be very useful, and thats how it worked before, so I wouldn't undervalue it, especially in terms of 3.0.0 migration

[mweststrate]

Ha yeah makes me wonder, is get x () => this.y valid syntax? But anyway computed should still be supported as it is concinsistent with the modifiers approach.

[andykog]

Ha yeah makes me wonder, is get x () => this.y valid syntax?

I think, no :-) What makes you assume this?

[mweststrate]

This change can be tested using [email protected]

[mweststrate]

Closing this issue as [email protected] is now available, which addresses this issue. Changelog: https://github.com/mobxjs/mobx/blob/mobx3/CHANGELOG.md#300. The changes in more details: https://github.com/mobxjs/mobx/pull/725/files. Feel free to re-open if questions arise!

[HaveF]

@mweststrate It is very pleasure to hear that mobx 3.0 will be out. I was taken to this thread by use computed in 2.7.0's warning message:

[mobx] Deprecated:
In MobX 2.* passing a function without arguments to (extend)observable will automatically be inferred to be a computed value.
This behavior is ambiguous and will change in MobX 3 to create just an observable reference to the value passed in.
To disambiguate, please pass the function wrapped with a modifier: use 'computed(fn)' (for current behavior; automatic conversion), or 'asReference(fn)' (future behavior, just store reference) or 'action(fn)'.
Note that the idiomatic way to write computed properties is 'observable({ get propertyName() { ... }})'.
For more details, see https://github.com/mobxjs/mobx/issues/532)in: [email protected]

I just try to install 3.0.0-rc.1, but find it is a bit hard to understand how to upgrade the exist code base to this version. Maybe I should wait?

I also find the change log of 2.7.0, but still confused how to use with decorator(could you explain how to upgrade the example below? Example from the official doc):

class Timer {
    @observable start = Date.now();
    @observable current = Date.now();

    @computed get elapsedTime() {
        return (this.current - this.start) + "seconds"
    }

    @action tick() {
        this.current = Date.now()
    }
}

maybe create the new series of egghead videos will be great :grin:

[indivisable]

Anyone help upgrade this code?

...
@observable panResponder = null;

constructor() {
    this.initPanResponder();
}

@action initPanResponder() {
this.panResponder = PanResponder.create({
...

I tried this but then it does not get called correctly:

this.panResponder = computed(()=> PanResponder.create({

[mweststrate]

@HaveF @indivisable be aware of commenting on closed issues, comments are easily missed :)

@HaveF your example is valid in both MobX 2 & 3

@indivisable
Your question lacks some information to be clear, but I think @observable.ref panResponder = null; is what you need; panResponder is a build in RN thing afaik, so probably you don't want to convert that into an observable itself

[indivisable]

@mweststrate Thanks! By simply removing the observable seemed to do the trick.

//@observable panResponder = null;

[crossingAreed]

thanks @mweststrate