Replace Ember.Map/OrderedSet with native Map/Set classes

[Turbo87]

ember-data is currently using Ember.Map and Ember.OrderedSet, which are close approximations of the native Map and Set classes introduced in ES2015. It seems that ember-data is the only major user of these classes and Ember is not even using them itself anymore and would like to get rid of them.

Since 3.0 is around the corner it might make sense to reevaluate the usefulness of these polyfills as IE11 already has somewhat usable native Map and Set support (see http://kangax.github.io/compat-table/es6/#test-Map).

As some public methods of ember-data return instances of Map and MapWithDefault this would probably have to be considered a breaking change 🤔

[rwjblue]

I submitted #5255 to migrate away from Ember.Map and Ember.MapWithDefault (to native Map), however after discussing with @hjdivad I believe that we will still have a need for @ember/ordered-set (the addon) as a custom data store for the ember-data relationship data (e.g. an array like with fast membership lookup for large relationships).

[Turbo87]

@rwjblue as mentioned in emberjs/ember-ordered-set#14 it seems that the differences between OrderedSet and Set are quite small, what is the specific difference that makes it necessary to keep OrderedSet around?

[hjdivad]

@Turbo87 https://github.com/emberjs/data/blob/master/addon/-private/system/ordered-set.js#L19

The order is not always insertion order. When inserting into a hasMany it is possible to insert at an arbitrary index. The relationships code currently assumes its set members has the same order as the many array.

[Turbo87]

@hjdivad okay, so we are actually talking about EmberData.OrderedSet 😉

[Turbo87]

this is somewhat important though because in that case the code for OrderedSet could just live inside of Ember Data instead of having a dedicated addon just for that class

[rwjblue]

@Turbo87 - Confirm, but I was just going to use the addon simply because it was already done and tested (thanks!). It also keeps the specific things needed here much simpler to reason about (e.g. the logic to avoid duplicating if Ember.OrderedSet is present).