How to use constants with ngSwitchCase

I have found multiple posts including ngSwitchCase in angular 2 instead of ngSwitchWhen, How to bind to '*ngSwitchCase', and Angular 2 - ngSwitchCase. Google wasn't helpful at all.

I am trying to create a simple form for entering search criteria. The first component is a select box and the second component an input box. Depending on the type of search you're doing, I want to use a different input for email, phone number, etc.

I'm feeding my select from constants defined in my form.

const SEARCH_BY_EMAIL = 'email';
const SEARCH_BY_PHONE = 'phone';
const SEARCH_BY_POSTAL_CODE = 'postalCode';

@Component({
  selector: 'app-choose-search-criteria',
  templateUrl: './choose-search-criteria.component.html',
  styleUrls: ['./choose-search-criteria.component.css']
})
export class ChooseSearchCriteriaComponent implements OnInit {

  searchTypes = [
      {value: SEARCH_BY_EMAIL, label: 'Email'},
      {value: SEARCH_BY_PHONE, label: 'Phone Number'},
      {value: SEARCH_BY_POSTAL_CODE, label: 'Zip Code'}
    ];
  searchBy: string;
  searchValue = '';

  constructor(protected dialogRef: MatDialogRef<ChooseSearchCriteriaComponent>,
              @Inject(MAT_DIALOG_DATA) public data: ChooseCriteriaDialogData) { }

  ngOnInit() {
  }

}

<h2>Enter Search Values</h2>
<div class="formFields">
  <mat-form-field>
    <mat-label>Search By</mat-label>
    <mat-select [(value)]="searchBy">
      <mat-option *ngFor="let searchType of searchTypes" [value]="searchType.value">
        {{searchType.label}}
      </mat-option>
    </mat-select>
  </mat-form-field>
  <div [ngSwitch]="searchBy">
    <mat-form-field *ngSwitchCase="SEARCH_BY_EMAIL">
      <input matInput placeholder="Enter Email Address" type="email" [(ngModel)]="searchValue"/>
    </mat-form-field>
    <mat-form-field *ngSwitchCase="SEARCH_BY_PHONE">
      <input matInput placeholder="Enter Phone Number" type="number" [(ngModel)]="searchValue"/>
    </mat-form-field>
    <mat-form-field *ngSwitchCase="SEARCH_BY_POSTAL_CODE">
      <input matInput placeholder="Enter Zip Code" type="number" [(ngModel)]="searchValue"/>
    </mat-form-field>

    <p *ngSwitchDefault>Select how you wish to search.</p>
  </div>
</div>

Problem is that it doesn't seem to be finding my constants on the ngSwitchCase. I've also tried {SEARCH_BY_POSTAL_CODE} and {{SEARCH_BY_POSTAL_CODE}} but these don't seem to work either.

So, I'm stuck. Advice, please?

Move constants inside of component class as a readonly fields.

From template you can reference only properties and methods of component's class.