feat: extract createSelector function for public api

[markwhitfeld]

Implements solution proposed in #426 to expose the createSelector function.
Provides a solution for #413.

It allows for this sort of syntax, enabling a static form of parameterized selectors:

@State<ConfigStateModel>({
  name: 'config',
  defaults: { clients: { schema: {} }, incomes: { schema: {} } }
})
export class ConfigState {
  static getSchema(type: keyof ConfigStateModel) {
    return createSelector([ConfigState], (state: ConfigStateModel) => state[type].schema);
  }
}

@Component(...)
export class ClientsListComponent {

  @Select(ConfigState.getSchema('clients'))
  public clientSchema$: Observable<any>;

}

[deebloo]

I think this is a good idea

[markwhitfeld]

The integration tests failed in a strange way (looks like a server error):
https://circleci.com/gh/ngxs/store/3541

Rewrote commit and pushed again to get a rebuild going and got the same error:
https://circleci.com/gh/ngxs/store/3544

It works locally so I'm not sure what the issue is here. Looks like missing pollyfills or something

[markwhitfeld]

Added more tests as part of this and now we have broken the 100 tests mark!

[deebloo]

@markwhitfeld this is actually a bit different then I was thinking. still poking at it

[markwhitfeld]

@deebloo what were you thinking? I'm interested in what other use cases for a createSelector that there may be

[amcdnl]

LGTM - what were u thinking Danny?

Make sure to update the docs.

[deebloo]

I still don't like pulling one state class into another. but I also don't see a way around it if we want to do something like this

[amcdnl]

@markwhitfeld - Can u PR docs for this?

[juliusstoerrle]

Hi! When would I choose this over the earlier introduced dynmic selector pattern (@Selector() static foo(state) { return (arg) => {}; })?

Main benefit I see is the use in @Select() and the reduced boilerplate which was introduced by the .pipe(map(...))? Art there any downsides to using this new method?

[markwhitfeld]

@juliusstoerrle See the docs added in PR #511
It clarifies the difference between lazy and dynamic selectors (the existing type being called 'lazy' and this new type 'dynamic').