refactor(cdk-experimental/selection): fix strict property initialization errors

Updates the code to be compatible with strict property initialization.

Author: crisbeto

src/cdk-experimental/selection/selection-column.ts

@@ -79,11 +79,11 @@ export class CdkSelectionColumn<T> implements OnInit, OnDestroy {
 
     this._syncColumnDefName();
   }
-  private _name: string;
+  private _name!: string;
 
-  @ViewChild(CdkColumnDef, {static: true}) private readonly _columnDef: CdkColumnDef;
-  @ViewChild(CdkCellDef, {static: true}) private readonly _cell: CdkCellDef;
-  @ViewChild(CdkHeaderCellDef, {static: true}) private readonly _headerCell: CdkHeaderCellDef;
+  @ViewChild(CdkColumnDef, {static: true}) private readonly _columnDef!: CdkColumnDef;
+  @ViewChild(CdkCellDef, {static: true}) private readonly _cell!: CdkCellDef;
+  @ViewChild(CdkHeaderCellDef, {static: true}) private readonly _headerCell!: CdkHeaderCellDef;
 
   ngOnInit() {
     if (!this.selection && (typeof ngDevMode === 'undefined' || ngDevMode)) {

src/cdk-experimental/selection/selection-toggle.ts

@@ -33,7 +33,7 @@ export class CdkSelectionToggle<T> implements OnDestroy, OnInit {
   private _controlValueAccessors = inject(NG_VALUE_ACCESSOR, {optional: true, self: true});
 
   /** The value that is associated with the toggle */
-  @Input('cdkSelectionToggleValue') value: T;
+  @Input('cdkSelectionToggleValue') value!: T;
 
   /** The index of the value in the list. Required when used with `trackBy` */
   @Input('cdkSelectionToggleIndex')

src/cdk-experimental/selection/selection.spec.ts

@@ -434,7 +434,7 @@ class ListWithMultiSelection {
   private readonly _elementRef = inject(ElementRef);
   private readonly _cdr = inject(ChangeDetectorRef);
 
-  @ViewChild(CdkSelection) cdkSelection: CdkSelection<string>;
+  @ViewChild(CdkSelection) cdkSelection!: CdkSelection<string>;
 
   data = ['apple', 'banana', 'cherry', 'durian'];
 
@@ -498,7 +498,7 @@ class ListWithSingleSelection {
   private readonly _elementRef = inject(ElementRef);
   private readonly _cdr = inject(ChangeDetectorRef);
 
-  @ViewChild(CdkSelection) cdkSelection: CdkSelection<string>;
+  @ViewChild(CdkSelection) cdkSelection!: CdkSelection<string>;
 
   data = ['apple', 'banana', 'cherry', 'durian'];
   selectionChange?: SelectionChange<string>;
@@ -539,7 +539,7 @@ class MultiSelectTableWithSelectionColumn {
   readonly elementRef = inject(ElementRef);
   private readonly _cdr = inject(ChangeDetectorRef);
 
-  @ViewChild(CdkSelection) cdkSelection: CdkSelection<string>;
+  @ViewChild(CdkSelection) cdkSelection!: CdkSelection<string>;
 
   columns = ['select', 'name'];
   data = ['apple', 'banana', 'cherry', 'durian'];
@@ -606,7 +606,7 @@ class SingleSelectTableWithSelectionColumn {
   readonly elementRef = inject(ElementRef);
   private readonly _cdr = inject(ChangeDetectorRef);
 
-  @ViewChild(CdkSelection) cdkSelection: CdkSelection<string>;
+  @ViewChild(CdkSelection) cdkSelection!: CdkSelection<string>;
 
   columns = ['select', 'name'];
   data = ['apple', 'banana', 'cherry', 'durian'];

src/cdk-experimental/selection/selection.ts

@@ -34,7 +34,7 @@ import {SelectableWithIndex, SelectionChange, SelectionSet} from './selection-se
   exportAs: 'cdkSelection',
 })
 export class CdkSelection<T> implements OnInit, AfterContentChecked, CollectionViewer, OnDestroy {
-  viewChange: Observable<ListRange>;
+  viewChange!: Observable<ListRange>;
 
   @Input()
   get dataSource(): TableDataSource<T> {
@@ -45,9 +45,9 @@ export class CdkSelection<T> implements OnInit, AfterContentChecked, CollectionV
       this._switchDataSource(dataSource);
     }
   }
-  private _dataSource: TableDataSource<T>;
+  private _dataSource!: TableDataSource<T>;
 
-  @Input('trackBy') trackByFn: TrackByFunction<T>;
+  @Input('trackBy') trackByFn!: TrackByFunction<T>;
 
   /** Whether to support multiple selection */
   @Input('cdkSelectionMultiple')
@@ -57,20 +57,20 @@ export class CdkSelection<T> implements OnInit, AfterContentChecked, CollectionV
   set multiple(multiple: BooleanInput) {
     this._multiple = coerceBooleanProperty(multiple);
   }
-  protected _multiple: boolean;
+  protected _multiple: boolean = false;
 
   /** Emits when selection changes. */
   @Output('cdkSelectionChange') readonly change = new EventEmitter<SelectionChange<T>>();
 
   /** Latest data provided by the data source. */
-  private _data: T[] | readonly T[];
+  private _data!: T[] | readonly T[];
 
   /** Subscription that listens for the data provided by the data source.  */
-  private _renderChangeSubscription: Subscription | null;
+  private _renderChangeSubscription: Subscription | null = null;
 
   private _destroyed = new Subject<void>();
 
-  private _selection: SelectionSet<T>;
+  private _selection!: SelectionSet<T>;
 
   private _switchDataSource(dataSource: TableDataSource<T>) {
     this._data = [];