extract uniqBy as generic method and reuse internally

packages/@ember/object/lib/computed/reduce_computed_macros.js

@@ -3,7 +3,7 @@
 */
 import { assert } from '@ember/debug';
 import { get, ComputedProperty, addObserver, removeObserver, getProperties } from 'ember-metal';
-import { compare, isArray, A as emberA } from 'ember-runtime';
+import { compare, isArray, A as emberA, uniqBy as uniqByArray } from 'ember-runtime';
 
 function reduceMacro(dependentKey, callback, initialValue, name) {
   assert(
@@ -495,19 +495,8 @@ export function uniqBy(dependentKey, propertyKey) {
 
   let cp = new ComputedProperty(
     function() {
-      let uniq = emberA();
       let list = get(this, dependentKey);
-      if (isArray(list)) {
-        let seen = new Set();
-        list.forEach(item => {
-          let val = get(item, propertyKey);
-          if (!seen.has(val)) {
-            seen.add(val);
-            uniq.push(item);
-          }
-        });
-      }
-      return uniq;
+      return isArray(list) ? uniqByArray(list, propertyKey) : emberA();
     },
     { dependentKeys: [`${dependentKey}.[]`], readOnly: true }
   );

packages/ember-runtime/index.js

@@ -28,6 +28,6 @@ export { default as Evented } from './lib/mixins/evented';
 export { default as PromiseProxyMixin } from './lib/mixins/promise_proxy';
 
 export { default as RSVP, onerrorDefault } from './lib/ext/rsvp'; // just for side effect of extending Ember.RSVP
-export { isArray, typeOf } from './lib/utils';
+export { isArray, typeOf, uniqBy } from './lib/utils';
 
 import './lib/ext/function'; // just for side effect of extending Function.prototype

packages/ember-runtime/lib/mixins/array.js

@@ -30,6 +30,7 @@ import Copyable from '../mixins/copyable';
 import copy from '../copy';
 import EmberError from '@ember/error';
 import MutableEnumerable from './mutable_enumerable';
+import { uniqBy } from '../utils';
 
 const EMPTY_ARRAY = Object.freeze([]);
 const EMBER_ARRAY = symbol('EMBER_ARRAY');
@@ -1002,17 +1003,7 @@ const ArrayMixin = Mixin.create(Enumerable, {
     @public
   */
   uniq() {
-    let ret = A();
-
-    let seen = new Set();
-    this.forEach(item => {
-      if (!seen.has(item)) {
-        seen.add(item);
-        ret.push(item);
-      }
-    });
-
-    return ret;
+    return uniqBy(this);
   },
 
   /**
@@ -1030,18 +1021,7 @@ const ArrayMixin = Mixin.create(Enumerable, {
   */
 
   uniqBy(key) {
-    let ret = A();
-    let seen = new Set();
-
-    this.forEach(item => {
-      let val = get(item, key);
-      if (!seen.has(val)) {
-        seen.add(val);
-        ret.push(item);
-      }
-    });
-
-    return ret;
+    return uniqBy(this, key);
   },
 
   /**

packages/ember-runtime/lib/utils.js

@@ -1,8 +1,9 @@
 import { DEBUG } from '@glimmer/env';
-import { PROXY_CONTENT } from 'ember-metal';
+import { PROXY_CONTENT, get } from 'ember-metal';
 import { HAS_NATIVE_PROXY } from 'ember-utils';
-import EmberArray from './mixins/array';
+import EmberArray, { A } from './mixins/array';
 import EmberObject from './system/object';
+import { assert } from '@ember/debug';
 
 // ........................................
 // TYPING & ARRAY MESSAGING
@@ -168,3 +169,23 @@ export function typeOf(item) {
 
   return ret;
 }
+
+const identityFunction = item => item;
+
+export function uniqBy(array, key = identityFunction) {
+  assert(`first argument passed to \`uniqBy\` should be array`, isArray(array));
+
+  let ret = A();
+  let seen = new Set();
+  let getter = typeof key === 'function' ? key : get;
+
+  array.forEach(item => {
+    let val = getter(item, key);
+    if (!seen.has(val)) {
+      seen.add(val);
+      ret.push(item);
+    }
+  });
+
+  return ret;
+}