Rebase and improve type checking by ensuring comparator is a function

Author: ppham27

src/lib/select/select.spec.ts

@@ -2433,34 +2433,27 @@ describe('MdSelect', () => {
     beforeEach(async(() => {
       fixture = TestBed.createComponent(NgModelCompareWithSelect);
       instance = fixture.componentInstance;
-      spyOn(instance, 'compareByReference').and.callThrough();
       fixture.detectChanges();
     }));
 
-    const testCompareByReferenceBehavior = () => {
-      it('should initialize with no selection despite having a value', () => {
-        expect(instance.selectedFood.value).toBe('pizza-1');
-        expect(instance.select.selected).toBeUndefined();
-      });
-
-      it('should not update the selection when changing the value', async(() => {
-        instance.options.first._selectViaInteraction();
-        fixture.detectChanges();
-        fixture.whenStable().then(() => {
-          expect(instance.selectedFood.value).toEqual('steak-0');
-          expect(instance.select.selected).toBeUndefined();
-        });
-      }));
-    };
-
-    it('should not use the comparator', () => {
-      expect(instance.compareByReference).not.toHaveBeenCalled();
+    it('should have a selection', () => {
+      const selectedOption = instance.select.selected as MdOption;
+      expect(selectedOption.value.value).toEqual('pizza-1');
     });
 
-    testCompareByReferenceBehavior();
+    it('should update when making a new selection', async(() => {
+      instance.options.last._selectViaInteraction();
+      fixture.detectChanges();
+      fixture.whenStable().then(() => {
+        const selectedOption = instance.select.selected as MdOption;
+        expect(instance.selectedFood.value).toEqual('tacos-2');
+        expect(selectedOption.value.value).toEqual('tacos-2');
+      });
+    }));
 
     describe('when comparing by reference', () => {
       beforeEach(async(() => {
+        spyOn(instance, 'compareByReference').and.callThrough();
         instance.useCompareByReference();
         fixture.detectChanges();
       }));
@@ -2469,30 +2462,32 @@ describe('MdSelect', () => {
         expect(instance.compareByReference).toHaveBeenCalled();
       });
 
-      testCompareByReferenceBehavior();
-    });
-
-    describe('when comparing by value', () => {
-      beforeEach(async(() => {
-        instance.useCompareByValue();
-        fixture.detectChanges();
-      }));
-
-      it('should have a selection', () => {
-        const selectedOption = instance.select.selected as MdOption;
-        expect(selectedOption.value.value).toEqual('pizza-1');
+      it('should initialize with no selection despite having a value', () => {
+        expect(instance.selectedFood.value).toBe('pizza-1');
+        expect(instance.select.selected).toBeUndefined();
       });
 
-      it('should update when making a new selection', async(() => {
-        instance.options.last._selectViaInteraction();
+      it('should not update the selection when changing the value', async(() => {
+        instance.options.first._selectViaInteraction();
         fixture.detectChanges();
         fixture.whenStable().then(() => {
-          const selectedOption = instance.select.selected as MdOption;
-          expect(instance.selectedFood.value).toEqual('tacos-2');
-          expect(selectedOption.value.value).toEqual('tacos-2');
+          expect(instance.selectedFood.value).toEqual('steak-0');
+          expect(instance.select.selected).toBeUndefined();
         });
       }));
     });
+
+    describe('when using a non-function comparator', () => {
+      beforeEach(() => {
+        instance.useNullComparator();
+      });
+
+      it('should throw an error', () => {
+        expect(() => {
+          fixture.detectChanges();
+        }).toThrowError('compareWith must be a function, but received null');
+      });
+    });
   });
 });
 
@@ -2958,7 +2953,7 @@ class NgModelCompareWithSelect {
     { value: 'tacos-2', viewValue: 'Tacos' },
   ];
   selectedFood: {value: string, viewValue: string} = { value: 'pizza-1', viewValue: 'Pizza' };
-  comparator: (f1: any, f2: any) => boolean;
+  comparator: ((f1: any, f2: any) => boolean)|null = this.compareByValue;
 
   @ViewChild(MdSelect) select: MdSelect;
   @ViewChildren(MdOption) options: QueryList<MdOption>;
@@ -2967,6 +2962,8 @@ class NgModelCompareWithSelect {
 
   useCompareByReference() { this.comparator = this.compareByReference; }
 
+  useNullComparator() { this.comparator = null; }
+
   compareByValue(f1: any, f2: any) { return f1 && f2 && f1.value === f2.value; }
 
   compareByReference(f1: any, f2: any) { return f1 === f2; }

src/lib/select/select.ts

@@ -293,11 +293,15 @@ export class MdSelect extends _MdSelectMixinBase implements AfterContentInit, On
   @Input()
   get compareWith() { return this._compareWith; }
   set compareWith(fn: (o1: any, o2: any) => boolean) {
+    if (typeof fn !== 'function') {
+      throw new TypeError(
+        `compareWith must be a function, but received ${JSON.stringify(fn)}`);
+    }
+    this._compareWith = fn;
     if (this._selectionModel) {
       // A different comparator means the selection could change.
       this._initializeSelection();
     }
-    this._compareWith = fn;
   }
 
   /** Whether to float the placeholder text. */