Update mobx computed value error

[fusepilot]

Reproduction: http://codepen.io/fusepilot/pen/mOOgWX

When deserializing back to a mobx computed value using deserializeState() in example 7, I get this error:

Invariant failed: [ComputedValue 'Box@1870.area'] It is not possible to assign a new value to a computed value.

I was expecting update to ignore setting computed values. But maybe that requires serializr to have too much knowledge of mobx's inner workings. Not sure.

Is this a bug? Or is there a proper way to avoid this problem when updating?

[mweststrate]

Conceptually, one should usually not need to serialize computed values. Since it is derived data there is often no need to store it. But if you want to serialize it, giving it a setter that doesn't do anything (or does actually something useful), should fix your problem, e.g.:

@serializable @computed get prop() { 
  return expr
}
set prop(v) {
  // ignore updates during de-serialization
}

[fusepilot]

Then the problem becomes:

Uncaught Error: [mobx] Invariant failed: @observable properties cannot have a setter.

http://codepen.io/fusepilot/pen/eBvMMK

Conceptually, one should usually not need to serialize computed values

Right, but it is useful when you just want to flush the entire state including computed values to json and not have to duplicate the computed function in the code receiving it.

[mweststrate]

What mobx version are you using? I think setters for computed properties were only introduced in 2.6 or later

[fusepilot]

Yeah, the codepen I was using for the reproductions was using 2.0.0. Updated to 2.6.3 and it works. Thanks!