Angular Syntax: How to use ng-repeat $index in expression - angularjs

Question

I have following code:
<form name="reviewForm_{{$index}}" ng-controller="reviewController as reviewCtrl" ng-submit="reviewCtrl.addReview(product)" novalidate>
<blockquote class="newReview">
<b>Stars {{reviewCtrl.review.stars}}</b>
<p>{{reviewCtrl.review.comment}}</p>
<cite>{{reviewCtrl.review.author}}</cite>
</blockquote>
<select class="form-control" ng-model="reviewCtrl.review.stars">
<option value="1">1 star</option>
<option value="1">2 stars</option>
<option value="1">3 stars</option>
<option value="1">4 stars</option>
<option value="1">5 stars</option>
</select><br />
<textarea ng-model="reviewCtrl.review.comment" required></textarea>
<label>by:</label>
<input type="text" ng-model="reviewCtrl.review.author" required /><br />
<div>reviewForm is {{reviewForm_$index.$valid}}</div>
<input class="btn btn-primary btn-large" type="submit" value="Submit" />
</form>
The Form above lies within a ng-repeat and has the name reviewForm_$index.
That works fine. So it will give reviewForm_0, reviewForm_1 and so on.
Now I would like to check if the form is valid with {{reviewForm_$index_$valid}}.
For some reason it doesn't show anything.
Do I have the wrong syntax?

Answer 1

Actually you are trying to access a property that does not exists since reviewform_$index will be treated as a form name not a variable. So change your code to something like this:
<div>reviewForm is {{reviewCtrl['reviewForm_' + $index].$valid}}</div>
That will work!!

Answer 2

Ok, I got it to work thanks to #klode.
Here my solution:
<form name="reviewForm" ng-controller="reviewController as reviewCtrl" ng-submit="reviewCtrl.addReview(product)" novalidate>
<blockquote class="newReview">
<b>Stars {{reviewCtrl.review.stars}}</b>
<p>{{reviewCtrl.review.comment}}</p>
<cite>{{reviewCtrl.review.author}}</cite>
</blockquote>
<select class="form-control" ng-model="reviewCtrl.review.stars">
<option value="1">1 star</option>
<option value="2">2 stars</option>
<option value="3">3 stars</option>
<option value="4">4 stars</option>
<option value="5">5 stars</option>
</select><br />
<textarea ng-model="reviewCtrl.review.comment" required></textarea>
<label>by:</label>
<input type="text" ng-model="reviewCtrl.review.author" required /><br />
<div>reviewForm is {{reviewForm.$valid}}</div>
<input class="btn btn-primary btn-large" type="submit" value="Submit" />
</form>
As explained by Klode can I leave the form name without the $index trailer and address the form's $valid property each loop via it's name just so: reviewForm.$valid