Cannot extend Map

[philipp-sorin]

Hey,
Mobx behaves incorrectly with classes extended from build-ins like Map<K, V>
For example (TS)

class StringToStringMap extends Map<string, string> {
  public findOne(id: string): Optional<string> {
    /// code
  }
 }

class Store  {
  @observable
  public stringToStringMap: StringToStringMap  = new StringToStringMap(); 
  // actual type is ObservableMap, method findOne is lost

  @action
  public doStuffWithString(someString: string) {
    this.stringToStringMap.findOne(someString); // throws an error TypeError: findOne is not a function
  } 
}

[fi3ework]

I test your code and it works fine. My TS version is 3.2.2.

update: I was wrong. I only checked if TS is working fine. However, it goes fine because StringToStringMap is an instance of StringToStringMap. There's still will be an error as you described in runtime.

[philipp-sorin]

Sounds strange because test function is written like value instanceof Map which satisfies my case

[mweststrate]

By default ES6 maps will be converted into observable maps. If you want to skip that behavior, use `@observable.ref` instead of `@observable`, and the map itself will not be turned into an observable Op do 3 jan. 2019 om 13:22 schreef philipp-sorin <[email protected]>:

…

Sounds starag because if test function is written like value instanceof Map which is satisfy my case — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#1858 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABvGhHLeUNY_YBjnLh-V3YhT83hSMlZ5ks5u_fYRgaJpZM4ZnYsb> .

[philipp-sorin]

@mweststrate
But it's not a direct Map, it's a sub type of the Map.
It should rather throw an Error if it cannot be converted, but silently change subtype to another subtype of base class looks like not good idea.

Because now, instead of extending Map and creating own observable using Atom, I have to write composite for Map. And this leads to the loss of some features, such as instanceof

[mweststrate]

Agreed, PR welcome :) I don't think we had a case before where someone used a subclass of a Map Op do 3 jan. 2019 om 14:12 schreef philipp-sorin <[email protected]>:

…

@mweststrate <https://github.com/mweststrate> But it's not a direct Map, it's a sub type of the Map. It should rather throw an Error if it cannot be converted, but silently change subtype to another subtype of base class looks like not good idea. Because now, instead of extending Map and creating own observable using Atom, I have to write composite for Map. And this leads to the loss of some features, such as instanceof — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1858 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABvGhLY3OTLD14oHhJS-ohkGAHMVqZvTks5u_gG-gaJpZM4ZnYsb> .

[philipp-sorin]

@mweststrate
Ok, maybe check it later when I will have time, so the issue seems to be closed by now?
Or should it be a feature request?

[mweststrate]

I think we can leave the issue open for now and rename it, to throw in such cases :) Op vr 4 jan. 2019 om 11:53 schreef philipp-sorin <[email protected]>:

…

@mweststrate <https://github.com/mweststrate> Ok, maybe check it later when I will have time, so the issue seems to be closed by now? Or should it be a feature request? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1858 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABvGhIS9uBnfjTZukQm1JaGrH5feJb_Tks5u_zK_gaJpZM4ZnYsb> .

[mweststrate]

Subclassing Map will be forbidden in the next version, as inheritance trees will be lost during cloning. Instead, use generic utilities like:

public findOne(map someMap, id: string): Optional<string> {
  // code operation on map
}

[mweststrate]

Addressed and released in 4.9.0 / 5.9.0

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs or questions.