feat(select): add compareWith Input for object value comparison (#11965)

fixes #6625

src/components/select/select.ts

@@ -123,6 +123,31 @@ import { SelectPopover, SelectPopoverOption } from './select-popover-component';
  * };
  * ```
  *
+ * ### Object Value References
+ *
+ * When using objects for select values, it is possible for the identities of these objects to
+ * change if they are coming from a server or database, while the selected value's identity
+ * remains the same. For example, this can occur when an existing record with the desired object value
+ * is loaded into the select, but the newly retrieved select options now have different identities. This will
+ * result in the select appearing to have no value at all, even though the original selection in still intact.
+ *
+ * Using the `compareWith` `Input` is the solution to this problem
+ *
+ * ```html
+ * <ion-item>
+ *   <ion-label>Employee</ion-label>
+ *   <ion-select [(ngModel)]="employee" [compareWith]="compareFn">
+ *     <ion-option *ngFor="let employee of employees" [value]="employee">{{employee.name}}</ion-option>
+ *   </ion-select>
+ * </ion-item>
+ * ```
+ *
+ * ```ts
+ * compareFn(e1: Employee, e2: Employee): boolean {
+ *   return e1 && e2 ? e1.id === e2.id : e1 === e2;
+ * }
+ * ```
+ *
  * @demo /docs/demos/src/select/
  */
 @Component({
@@ -153,6 +178,7 @@ export class Select extends BaseInput<any> implements OnDestroy {
   _overlay: ActionSheet | Alert | Popover;
   _texts: string[] = [];
   _text: string = '';
+  _compareWith: (o1: any, o2: any) => boolean = isCheckedProperty;
 
   /**
    * @input {string} The text to display on the cancel button. Default: `Cancel`.
@@ -187,6 +213,18 @@ export class Select extends BaseInput<any> implements OnDestroy {
    */
   @Input() selectedText: string = '';
 
+  /**
+   * @input {Function} The function that will be called to compare object values
+   */
+  @Input()
+  set compareWith(fn: (o1: any, o2: any) => boolean) {
+    if (typeof fn !== 'function') {
+      throw new Error(`compareWith must be a function, but received ${JSON.stringify(fn)}`);
+    }
+    this._compareWith = fn;
+  }
+
+
   /**
    * @output {any} Emitted when the selection was cancelled.
    */
@@ -448,7 +486,7 @@ export class Select extends BaseInput<any> implements OnDestroy {
       this._options.forEach(option => {
         // check this option if the option's value is in the values array
         option.selected = this.getValues().some(selectValue => {
-          return isCheckedProperty(selectValue, option.value);
+          return this._compareWith(selectValue, option.value);
         });
 
         if (option.selected) {