title: Got interpolation ({{}}) where expression was expected
body: <p>I have the following HTML but i get the the exception. How to fix it ?</p>
  
  <blockquote>
    <p>Parser Error: Got interpolation ({{}}) where expression was expected
    at column 48 in
    [!(editForm.controls.field_item_exportExpression_{{i}}?.dirty &amp;&amp;
    editForm.controls.field_item_exportExpression_{{i}}?.invalid)]</p>
  </blockquote>
  
  <pre><code>&lt;div class="form-group"&gt;
    &lt;label class="form-control-label" for="field_exportExpression"&gt;exportExpression&lt;/label&gt;
    &lt;input class="form-control" type="text" id="field_item_exportExpression_{{i}}" name="item_exportExpression_{{i}}" [(ngModel)]="datatype.items[i].exportExpression" required&gt;
    &lt;div [hidden]="!(editForm.controls.field_item_exportExpression_{{i}}?.dirty &amp;&amp; editForm.controls.field_item_exportExpression_{{i}}?.invalid)"&gt;
     &lt;small class="form-text text-danger" [hidden]="!editForm.controls.field_item_exportExpression_{{i}}?.errors?.required" dpTranslate="dataconfiguration.validation.required"&gt; This field is
                              required. &lt;/small&gt;
   &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>The following is not working. Saying unwanted token <code>[</code> found.</p>
  
  <pre><code>[hidden]="!editForm.controls.['item_exportExpression_' + i]?.errors?.required 
  </code></pre>
  
  <p>The following is not complaining about <code>[</code> but complaining <code>Cannot read property '0' of undefined</code></p>
  
  <pre><code> [hidden]="!editForm.controls.item_exportExpression_[ i]?.errors?.required 
  </code></pre>