title: Is there a .NET StringBuilder that uses UTF-8 directly?
body: <p>I have a performance sensitive scenario where I would like to write UTF-8 to a byte array.</p>
  
  <p>A quick glimpse on the .NET StringBuilder class has me believe that it only builds UTF-16 natively. Encoding.UTF8.GetBytes(str) means extra allocations and extra clock cycles that I am not willing to spend.</p>
  
  <p>Is there a native UTF-8 writer?</p>