Deprecate EmberObject

text/1234-deprecate-ember-object.md

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+---
+stage: accepted
+start-date:
+release-date:
+release-versions:
+teams: # delete teams that aren't relevant
+  - cli
+  - data
+  - framework
+  - learning
+  - steering
+  - typescript
+prs:
+  accepted: https://github.com/emberjs/rfcs/pull/1234 
+project-link:
+---
+
+<!---
+Directions for above:
+
+stage: Leave as is
+start-date: Fill in with today's date, 2032-12-01T00:00:00.000Z
+release-date: Leave as is
+release-versions: Leave as is
+teams: Include only the [team(s)](README.md#relevant-teams) for which this RFC applies
+prs:
+  accepted: Fill this in with the URL for the Proposal RFC PR
+project-link: Leave as is
+-->
+
+# Deprecate EmberObject 
+
+## Summary
+
+Deprecates `EmberObject` in a way that is initually opt-in, so people can more gradually prepare their codebase for the removal of `EmberObject`. 
+
+
+## Motivation
+
+`EmberObject` has had heavy use in the early days of Ember (pre-JavaScript having classes), and since classes shipped in 2015, the need for `EmberObject` has greatly diminished. 
+
+Removing `EmberObject` is one of the last steps in coercing codebases to be plain modern JavaScript.
+
+## Transition Path
+
+Unlike previous deprecations, this is targeting Ember 9, and will have a feature flag that removes all behavior related to `EmberObject`. This does require a lot of internal implementation in `ember-source`, but is needed anyway for the removal of `EmberObject`, ultimately.
+
+This will be the first deprecation that users will be able to preview the removal off.
+
+Leading up to v8, the feature flag will be "off":
+- deprecation logged for all EmberObject APIs (even thoose acessible through framework objects (get/set/etc))
+- EmberObject is still usable
+
+With the release of v8, and leading up to v9, the feature flag will be "on" by default:
+- EmberObject (and related APIs) is/are not usable, due to the feature flag removing all of the implementation
+- if users wish, the feature flag can be flipped back off, which brings back the EmberObject behavior along with the deprecations
+
+At `ember-source` v9, `EmberObject` is removed fully along with the feature flag.
+
+
+> [!NOTE]
+> This includes `@computed`, as `@computed` is part of the "Ember Object Model" of reactivity.
+
+
+Internally, implementation would likely be similar to how Mixins were initially deprecated -- copied to an "internal" file, and then the "public" version of `EmberObject` would override `init`, and provide the deprecations. 
+
+On the internal copy of `EmberObject`, we deprecate all the methods (`get`, / `set` / etc), so that the deprecations flow through to other framework classes such as `Route`, `Controller`, `Service`, etc.
+
+## How We Teach This
+
+> Would the acceptance of this proposal mean the Ember guides must be
+re-organized or altered? Does it change how Ember is taught to new users
+at any level?
+Does it mean we need to put effort into highlighting the replacement
+functionality more? What should we do about documentation, in the guides
+related to this feature?
+How should this deprecation be introduced and explained to existing Ember
+users?
+
+> Keep in mind the variety of learning materials: API docs, guides, blog posts, tutorials, etc.
+
+## Drawbacks
+
+keeping EmberObject is a drawback, because of the dozens of KB that come along with it.
+
+all codebases with old code probably have some usage of EmberObject remaining, so they need to migrate.
+
+## Alternatives
+
+- do nothing
+
+## Unresolved questions
+
+n/a