如何在ng-if中使用$ index

So I have this code below

所以我在下面有这个代码

<form name="registrationForm">
<div class="form-inline" ng-repeat="participant in participantsArray">
        <div class="form-group">
          <input ng-model="datas.name[$index+1]" name="name{{$index+1}}" required verify-name>
          <span ng-if="registrationForm.name+($index+1).$dirty && registrationForm.name+($index+1).$invalid">error</span>
        </div>
</div>
</form>
<form