Summary
This RFC proposes the deprecation of the following classes:
Ember.OrderedSetEmber.MapEmber.MapWithDefault
These classes need to be moved to an external addon given they are private classes and unused in Ember.js itself.
Motivation
These classes have not been used in Ember itself for a while now. They have always been private but they are used in a few addons, and in particular Ember Data is using them.
Transition Path
Ember.Map and Ember.MapWithDefault will be deprecated and not extracted, but not before the fix mentioned in the following paragraph is landed in Ember Data. There is already an addon with Ember.OrderedSet extracted (@ember/ordered-set).
Ember Data is quite likely the biggest project using these classes. There is already a PR that needs merging before deprecating Ember.Map and Ember.MapWithDefault https://github.com/emberjs/data/pull/5255. Ember Data still needs to migrate to @ember/ordered-set to its relationship logic.
Once Ember Data is updated to not use the classes from Ember, and that fix is released, the Ember.Map and Ember.MapWithDefault can be deprecated in Ember itself.
How We Teach This
These classes being private would make this simple than other deprecations. People were not supposed to be using a private API and the few that were, would just need to use a new addon.
This should not impact many codebases.
Drawbacks
This requires cooperation with Ember Data, the main user of these classes. It would be nice to have moved Ember Data to using the addon before releasing Ember with the deprecation so the average user does not see any deprecation warning.
Alternatives
Other option would be moving these classes to Ember Data itself or leaving things as they are now.