title: Array does not contain a definition for 'AsReadOnly'
body: <p>I am using C# with .NET Core 1.1 under OS X (target framework is <code>netstandard1.6</code>) and I am getting an odd error for a missing method.</p>
  
  <pre><code>using System;
  using System.Collections.ObjectModel;
  
  class Program
  {
      static void Main()
      {
          int[] array = { 1, 2, 3 };
          ReadOnlyCollection&lt;int&gt; result = Array.AsReadOnly(array);
      }
  }
  </code></pre>
  
  <p>Compilation of the program shown above results in the error</p>
  
  <pre><code>error CS0117: 'Array' does not contain a definition for 'AsReadOnly'
  </code></pre>
  
  <p>Is <code>AsReadOnly</code> not available in .NET Core or am I missing something else? </p>