title: Implement Span<T> in Unity
body: <p>I'm trying to use <a href="https://docs.microsoft.com/en-us/dotnet/api/system.span-1?view=netstandard-2.1" rel="nofollow noreferrer">Span</a> in Unity.</p>
  
  <p>I understand that <code>System.Memory</code> is not supported yet, but I'd like to implement it anyway.</p>
  
  <p>I directly downloaded the library from <a href="https://www.nuget.org/packages/System.Memory/" rel="nofollow noreferrer">NuGet</a>. I got the <code>System.Memory.dll</code> from netstandard2.0 folder in the nuget package and dragged it in the project Assets/Scripts folder.</p>
  
  <p>But I get this error, and I cannot use it in my IDE (Rider).</p>
  
  <blockquote>
    <p>Assembly 'Assets/System.Memory.dll' will not be loaded due
    to errors: Unable to resolve reference
    'System.Runtime.CompilerServices.Unsafe'. Is the assembly missing or
    incompatible with the current platform?</p>
  </blockquote>
  
  <p>My question is: how can I use Span in Unity?</p>
  
  <hr>
  
  <p><strong>Unity Version</strong>: Unity 2019.1.7f.<br>
  <strong>OS</strong>: Windows</p>