chore: make all event emitters / subjects readonly

src/lib/autocomplete/autocomplete-trigger.ts

@@ -131,7 +131,7 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
   private _closingActionsSubscription: Subscription;
 
   /** Stream of keyboard events that can close the panel. */
-  private _closeKeyEventStream = new Subject<void>();
+  private readonly _closeKeyEventStream = new Subject<void>();
 
   /** View -> model callback called when value changes */
   _onChange: (value: any) => void = () => {};
@@ -209,7 +209,7 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
   }
 
   /** Stream of autocomplete option selections. */
-  optionSelections: Observable<MatOptionSelectionChange> = defer(() => {
+  readonly optionSelections: Observable<MatOptionSelectionChange> = defer(() => {
     if (this.autocomplete && this.autocomplete.options) {
      return merge(...this.autocomplete.options.map(option => option.onSelectionChange));
     }

src/lib/autocomplete/autocomplete.ts

@@ -99,7 +99,7 @@ export class MatAutocomplete extends _MatAutocompleteMixinBase implements AfterC
   @Input() displayWith: ((value: any) => string) | null = null;
 
   /** Event that is emitted whenever an option from the list is selected. */
-  @Output() optionSelected: EventEmitter<MatAutocompleteSelectedEvent> =
+  @Output() readonly optionSelected: EventEmitter<MatAutocompleteSelectedEvent> =
       new EventEmitter<MatAutocompleteSelectedEvent>();
 
   /**

src/lib/button-toggle/button-toggle.ts

@@ -127,7 +127,7 @@ export class MatButtonToggleGroup extends _MatButtonToggleGroupMixinBase
    * Used to facilitate two-way data binding.
    * @docs-private
    */
-  @Output() valueChange = new EventEmitter<any>();
+  @Output() readonly valueChange = new EventEmitter<any>();
 
   /** Whether the toggle group is selected. */
   @Input()
@@ -142,7 +142,8 @@ export class MatButtonToggleGroup extends _MatButtonToggleGroupMixinBase
   }
 
   /** Event emitted when the group's value changes. */
-  @Output() change: EventEmitter<MatButtonToggleChange> = new EventEmitter<MatButtonToggleChange>();
+  @Output() readonly change: EventEmitter<MatButtonToggleChange> =
+      new EventEmitter<MatButtonToggleChange>();
 
   constructor(private _changeDetector: ChangeDetectorRef) {
     super();
@@ -357,7 +358,8 @@ export class MatButtonToggle implements OnInit, OnDestroy {
   }
 
   /** Event emitted when the group value changes. */
-  @Output() change: EventEmitter<MatButtonToggleChange> = new EventEmitter<MatButtonToggleChange>();
+  @Output() readonly change: EventEmitter<MatButtonToggleChange> =
+      new EventEmitter<MatButtonToggleChange>();
 
   constructor(@Optional() toggleGroup: MatButtonToggleGroup,
               @Optional() toggleGroupMultiple: MatButtonToggleGroupMultiple,

src/lib/checkbox/checkbox.ts

@@ -166,10 +166,11 @@ export class MatCheckbox extends _MatCheckboxMixinBase implements ControlValueAc
   @Input() name: string | null = null;
 
   /** Event emitted when the checkbox's `checked` value changes. */
-  @Output() change: EventEmitter<MatCheckboxChange> = new EventEmitter<MatCheckboxChange>();
+  @Output() readonly change: EventEmitter<MatCheckboxChange> =
+      new EventEmitter<MatCheckboxChange>();
 
   /** Event emitted when the checkbox's `indeterminate` value changes. */
-  @Output() indeterminateChange: EventEmitter<boolean> = new EventEmitter<boolean>();
+  @Output() readonly indeterminateChange: EventEmitter<boolean> = new EventEmitter<boolean>();
 
   /** The value attribute of the native input element */
   @Input() value: string;

src/lib/chips/chip-list.ts

@@ -305,14 +305,15 @@ export class MatChipList extends _MatChipListMixinBase implements MatFormFieldCo
   }
 
   /** Event emitted when the selected chip list value has been changed by the user. */
-  @Output() change: EventEmitter<MatChipListChange> = new EventEmitter<MatChipListChange>();
+  @Output() readonly change: EventEmitter<MatChipListChange> =
+      new EventEmitter<MatChipListChange>();
 
   /**
    * Event that emits whenever the raw value of the chip-list changes. This is here primarily
    * to facilitate the two-way binding for the `value` input.
    * @docs-private
    */
-  @Output() valueChange: EventEmitter<any> = new EventEmitter<any>();
+  @Output() readonly valueChange: EventEmitter<any> = new EventEmitter<any>();
 
   /** The chip components contained within this chip list. */
   @ContentChildren(MatChip) chips: QueryList<MatChip>;

src/lib/chips/chip.ts

@@ -137,27 +137,27 @@ export class MatChip extends _MatChipMixinBase implements FocusableOption, OnDes
   }
 
   /** Emits when the chip is focused. */
-  _onFocus = new Subject<MatChipEvent>();
+  readonly _onFocus = new Subject<MatChipEvent>();
 
   /** Emits when the chip is blured. */
-  _onBlur = new Subject<MatChipEvent>();
+  readonly _onBlur = new Subject<MatChipEvent>();
 
   /** Emitted when the chip is selected or deselected. */
-  @Output() selectionChange: EventEmitter<MatChipSelectionChange>
-      = new EventEmitter<MatChipSelectionChange>();
+  @Output() readonly selectionChange: EventEmitter<MatChipSelectionChange> =
+      new EventEmitter<MatChipSelectionChange>();
 
   /** Emitted when the chip is destroyed. */
-  @Output() destroyed = new EventEmitter<MatChipEvent>();
+  @Output() readonly destroyed = new EventEmitter<MatChipEvent>();
 
   /**
    * Emitted when the chip is destroyed.
    * @deprecated Use 'destroyed' instead.
    * @deletion-target 6.0.0
    */
-  @Output() destroy: EventEmitter<MatChipEvent> = this.destroyed;
+  @Output() readonly destroy: EventEmitter<MatChipEvent> = this.destroyed;
 
   /** Emitted when a chip is to be removed. */
-  @Output() removed: EventEmitter<MatChipEvent> = new EventEmitter<MatChipEvent>();
+  @Output() readonly removed: EventEmitter<MatChipEvent> = new EventEmitter<MatChipEvent>();
 
   /**
    * Emitted when a chip is to be removed.

src/lib/core/common-behaviors/error-state.ts

@@ -14,7 +14,7 @@ import {Subject} from 'rxjs/Subject';
 /** @docs-private */
 export interface CanUpdateErrorState {
   updateErrorState();
-  stateChanges: Subject<void>;
+  readonly stateChanges: Subject<void>;
   errorState: boolean;
   errorStateMatcher: ErrorStateMatcher;
 }
@@ -41,7 +41,7 @@ export function mixinErrorState<T extends Constructor<HasErrorState>>(base: T)
      * Stream that emits whenever the state of the input changes such that the wrapping
      * `MatFormField needs to run change detection.
      */
-    stateChanges = new Subject<void>();
+    readonly stateChanges = new Subject<void>();
 
     errorStateMatcher: ErrorStateMatcher;
 

src/lib/core/option/option.ts

@@ -112,10 +112,10 @@ export class MatOption implements AfterViewChecked {
   get disableRipple() { return this._parent && this._parent.disableRipple; }
 
   /** Event emitted when the option is selected or deselected. */
-  @Output() onSelectionChange = new EventEmitter<MatOptionSelectionChange>();
+  @Output() readonly onSelectionChange = new EventEmitter<MatOptionSelectionChange>();
 
   /** Emits when the state of the option changes and any parents have to be notified. */
-  _stateChanges = new Subject<void>();
+  readonly _stateChanges = new Subject<void>();
 
   constructor(
     private _element: ElementRef,

src/lib/datepicker/calendar-body.ts

@@ -79,7 +79,7 @@ export class MatCalendarBody {
   @Input() cellAspectRatio = 1;
 
   /** Emits when a new value is selected. */
-  @Output() selectedValueChange = new EventEmitter<number>();
+  @Output() readonly selectedValueChange = new EventEmitter<number>();
 
   _cellClicked(cell: MatCalendarCell): void {
     if (!this.allowDisabledSelection && !cell.enabled) {

src/lib/datepicker/calendar.ts

@@ -105,10 +105,10 @@ export class MatCalendar<D> implements AfterContentInit, OnDestroy, OnChanges {
   @Input() dateFilter: (date: D) => boolean;
 
   /** Emits when the currently selected date changes. */
-  @Output() selectedChange = new EventEmitter<D>();
+  @Output() readonly selectedChange = new EventEmitter<D>();
 
   /** Emits when any date is selected. */
-  @Output() _userSelection = new EventEmitter<void>();
+  @Output() readonly _userSelection = new EventEmitter<void>();
 
   /** Reference to the current month view component. */
   @ViewChild(MatMonthView) monthView: MatMonthView<D>;

src/lib/datepicker/datepicker-input.ts

@@ -165,12 +165,12 @@ export class MatDatepickerInput<D> implements AfterContentInit, ControlValueAcce
   private _disabled: boolean;
 
   /** Emits when a `change` event is fired on this `<input>`. */
-  @Output() dateChange: EventEmitter<MatDatepickerInputEvent<D>>
-      = new EventEmitter<MatDatepickerInputEvent<D>>();
+  @Output() readonly dateChange: EventEmitter<MatDatepickerInputEvent<D>> =
+      new EventEmitter<MatDatepickerInputEvent<D>>();
 
   /** Emits when an `input` event is fired on this `<input>`. */
-  @Output() dateInput: EventEmitter<MatDatepickerInputEvent<D>>
-      = new EventEmitter<MatDatepickerInputEvent<D>>();
+  @Output() readonly dateInput: EventEmitter<MatDatepickerInputEvent<D>> =
+      new EventEmitter<MatDatepickerInputEvent<D>>();
 
   /** Emits when the value changes (either due to user input or programmatic change). */
   _valueChange = new EventEmitter<D|null>();

src/lib/datepicker/datepicker-intl.ts

@@ -17,7 +17,7 @@ export class MatDatepickerIntl {
    * Stream that emits whenever the labels here are changed. Use this to notify
    * components if the labels have changed after initialization.
    */
-  changes: Subject<void> = new Subject<void>();
+  readonly changes: Subject<void> = new Subject<void>();
 
   /** A label for the calendar popup (used by screen readers). */
   calendarLabel = 'Calendar';

src/lib/datepicker/datepicker.ts

@@ -162,7 +162,7 @@ export class MatDatepicker<D> implements OnDestroy {
    * @deprecated Switch to the `dateChange` and `dateInput` binding on the input element.
    * @deletion-target 6.0.0
    */
-  @Output() selectedChanged: EventEmitter<D> = new EventEmitter<D>();
+  @Output() readonly selectedChanged: EventEmitter<D> = new EventEmitter<D>();
 
   /** Classes to be passed to the date picker panel. Supports the same syntax as `ngClass`. */
   @Input() panelClass: string | string[];
@@ -219,7 +219,7 @@ export class MatDatepicker<D> implements OnDestroy {
   _datepickerInput: MatDatepickerInput<D>;
 
   /** Emits when the datepicker is disabled. */
-  _disabledChange = new Subject<boolean>();
+  readonly _disabledChange = new Subject<boolean>();
 
   constructor(private _dialog: MatDialog,
               private _overlay: Overlay,

src/lib/datepicker/month-view.ts

@@ -68,10 +68,10 @@ export class MatMonthView<D> implements AfterContentInit {
   @Input() dateFilter: (date: D) => boolean;
 
   /** Emits when a new date is selected. */
-  @Output() selectedChange = new EventEmitter<D | null>();
+  @Output() readonly selectedChange = new EventEmitter<D | null>();
 
   /** Emits when any date is selected. */
-  @Output() _userSelection = new EventEmitter<void>();
+  @Output() readonly _userSelection = new EventEmitter<void>();
 
   /** The label for this month (e.g. "January 2017"). */
   _monthLabel: string;

src/lib/datepicker/multi-year-view.ts

@@ -68,7 +68,7 @@ export class MatMultiYearView<D> implements AfterContentInit {
   @Input() dateFilter: (date: D) => boolean;
 
   /** Emits when a new month is selected. */
-  @Output() selectedChange = new EventEmitter<D>();
+  @Output() readonly selectedChange = new EventEmitter<D>();
 
   /** Grid of calendar cells representing the currently displayed years. */
   _years: MatCalendarCell[][];

src/lib/datepicker/year-view.ts

@@ -63,7 +63,7 @@ export class MatYearView<D> implements AfterContentInit {
   @Input() dateFilter: (date: D) => boolean;
 
   /** Emits when a new month is selected. */
-  @Output() selectedChange = new EventEmitter<D>();
+  @Output() readonly selectedChange = new EventEmitter<D>();
 
   /** Grid of calendar cells representing the months of the year. */
   _months: MatCalendarCell[][];

src/lib/dialog/dialog-ref.ts

@@ -34,13 +34,13 @@ export class MatDialogRef<T, R = any> {
   disableClose: boolean | undefined = this._containerInstance._config.disableClose;
 
   /** Subject for notifying the user that the dialog has finished opening. */
-  private _afterOpen = new Subject<void>();
+  private readonly _afterOpen = new Subject<void>();
 
   /** Subject for notifying the user that the dialog has finished closing. */
-  private _afterClosed = new Subject<R | undefined>();
+  private readonly _afterClosed = new Subject<R | undefined>();
 
   /** Subject for notifying the user that the dialog has started closing. */
-  private _beforeClose = new Subject<R | undefined>();
+  private readonly _beforeClose = new Subject<R | undefined>();
 
   /** Result to be passed to afterClosed. */
   private _result: R | undefined;

src/lib/dialog/dialog.ts

@@ -66,8 +66,8 @@ export const MAT_DIALOG_SCROLL_STRATEGY_PROVIDER = {
 @Injectable()
 export class MatDialog {
   private _openDialogsAtThisLevel: MatDialogRef<any>[] = [];
-  private _afterAllClosedAtThisLevel = new Subject<void>();
-  private _afterOpenAtThisLevel = new Subject<MatDialogRef<any>>();
+  private readonly _afterAllClosedAtThisLevel = new Subject<void>();
+  private readonly _afterOpenAtThisLevel = new Subject<MatDialogRef<any>>();
   private _ariaHiddenElements = new Map<Element, string|null>();
 
   /** Keeps track of the currently-open dialogs. */
@@ -89,7 +89,7 @@ export class MatDialog {
    * Stream that emits when all open dialog have finished closing.
    * Will emit on subscribe if there are no open dialogs to begin with.
    */
-  afterAllClosed: Observable<void> = defer<void>(() => this.openDialogs.length ?
+  readonly afterAllClosed: Observable<void> = defer<void>(() => this.openDialogs.length ?
       this._afterAllClosed :
       this._afterAllClosed.pipe(startWith(undefined)));
 

src/lib/expansion/expansion-panel.ts

@@ -99,7 +99,7 @@ export class MatExpansionPanel extends _MatExpansionPanelMixinBase
   private _hideToggle = false;
 
   /** Stream that emits for changes in `@Input` properties. */
-  _inputChanges = new Subject<SimpleChanges>();
+  readonly _inputChanges = new Subject<SimpleChanges>();
 
   /** Optionally defined accordion the expansion panel belongs to. */
   accordion: MatAccordion;

src/lib/input/autosize.ts

@@ -38,7 +38,7 @@ import {Subject} from 'rxjs/Subject';
 export class MatTextareaAutosize implements AfterViewInit, DoCheck, OnDestroy {
   /** Keep track of the previous textarea value to avoid resizing when the value hasn't changed. */
   private _previousValue: string;
-  private _destroyed = new Subject<void>();
+  private readonly _destroyed = new Subject<void>();
 
   private _minRows: number;
   private _maxRows: number;

src/lib/input/input.ts

@@ -100,7 +100,7 @@ export class MatInput extends _MatInputMixinBase implements MatFormFieldControl<
    * Stream that emits whenever the state of the input changes such that the wrapping `MatFormField`
    * needs to run change detection.
    */
-  stateChanges = new Subject<void>();
+  readonly stateChanges = new Subject<void>();
 
   /** A name for this control that can be used by `mat-form-field`. */
   controlType = 'mat-input';

src/lib/list/selection-list.ts

@@ -158,7 +158,7 @@ export class MatListOption extends _MatListOptionMixinBase
    * @deprecated Use the `selectionChange` event on the `<mat-selection-list>` instead.
    * @deletion-target 6.0.0
    */
-  @Output() selectionChange: EventEmitter<MatListOptionChange> =
+  @Output() readonly selectionChange: EventEmitter<MatListOptionChange> =
     new EventEmitter<MatListOptionChange>();
 
   constructor(private _element: ElementRef,
@@ -301,7 +301,7 @@ export class MatSelectionList extends _MatSelectionListMixinBase implements Focu
   @ContentChildren(MatListOption) options: QueryList<MatListOption>;
 
   /** Emits a change event whenever the selected state of an option changes. */
-  @Output() selectionChange: EventEmitter<MatSelectionListChange> =
+  @Output() readonly selectionChange: EventEmitter<MatSelectionListChange> =
       new EventEmitter<MatSelectionListChange>();
 
   /** The currently selected options. */

src/lib/menu/menu-directive.ts

@@ -168,8 +168,8 @@ export class MatMenu implements AfterContentInit, MatMenuPanel, OnDestroy {
   set classList(classes: string) { this.panelClass = classes; }
 
   /** Event emitted when the menu is closed. */
-  @Output() closed: EventEmitter<void | 'click' | 'keydown'>
-      = new EventEmitter<void | 'click' | 'keydown'>();
+  @Output() readonly closed: EventEmitter<void | 'click' | 'keydown'> =
+      new EventEmitter<void | 'click' | 'keydown'>();
 
   /**
    * Event emitted when the menu is closed.

src/lib/menu/menu-item.ts

@@ -60,7 +60,7 @@ export class MatMenuItem extends _MatMenuItemMixinBase
   private _document: Document;
 
   /** Stream that emits when the menu item is hovered. */
-  _hovered: Subject<MatMenuItem> = new Subject<MatMenuItem>();
+  readonly _hovered: Subject<MatMenuItem> = new Subject<MatMenuItem>();
 
   /** Whether the menu item is highlighted. */
   _highlighted: boolean = false;

src/lib/menu/menu-trigger.ts

@@ -111,24 +111,24 @@ export class MatMenuTrigger implements AfterContentInit, OnDestroy {
   @Input('matMenuTriggerFor') menu: MatMenuPanel;
 
   /** Event emitted when the associated menu is opened. */
-  @Output() menuOpened: EventEmitter<void> = new EventEmitter<void>();
+  @Output() readonly menuOpened: EventEmitter<void> = new EventEmitter<void>();
 
   /**
    * Event emitted when the associated menu is opened.
    * @deprecated Switch to `menuOpened` instead
    * @deletion-target 6.0.0
    */
-  @Output() onMenuOpen: EventEmitter<void> = this.menuOpened;
+  @Output() readonly onMenuOpen: EventEmitter<void> = this.menuOpened;
 
   /** Event emitted when the associated menu is closed. */
-  @Output() menuClosed: EventEmitter<void> = new EventEmitter<void>();
+  @Output() readonly menuClosed: EventEmitter<void> = new EventEmitter<void>();
 
   /**
    * Event emitted when the associated menu is closed.
    * @deprecated Switch to `menuClosed` instead
    * @deletion-target 6.0.0
    */
-  @Output() onMenuClose: EventEmitter<void> = this.menuClosed;
+  @Output() readonly onMenuClose: EventEmitter<void> = this.menuClosed;
 
   constructor(private _overlay: Overlay,
               private _element: ElementRef,

src/lib/paginator/paginator-intl.ts

@@ -19,7 +19,7 @@ export class MatPaginatorIntl {
    * Stream that emits whenever the labels here are changed. Use this to notify
    * components if the labels have changed after initialization.
    */
-  changes: Subject<void> = new Subject<void>();
+  readonly changes: Subject<void> = new Subject<void>();
 
   /** A label for the page size selector. */
   itemsPerPageLabel: string = 'Items per page:';

src/lib/paginator/paginator.ts

@@ -101,7 +101,7 @@ export class MatPaginator implements OnInit, OnDestroy {
   @Input() hidePageSize = false;
 
   /** Event emitted when the paginator changes the page size or page index. */
-  @Output() page = new EventEmitter<PageEvent>();
+  @Output() readonly page = new EventEmitter<PageEvent>();
 
   /** Displayed set of page size options. Will be sorted and include current page size. */
   _displayedPageSizeOptions: number[];