title: Multiple Constructors in f# with property assignment
body: <p>I want to have a constructor that is blank and a constructor overload that accepts a parameter and assign it to a public property.</p>
  
  <p>This is where I am stuck:</p>
  
  <pre><code>type TemplateService() = 
      interface ITemplateService with
  
          //Properties
          member TemplateDirectory = ""
  
          //Constructors
          new (templateDirectory:string) = //Error here.
              if (templateDirectory == null) then
                  raise (new System.ArgumentNullException("templateDirectory"))
              TemplateDirectory = templateDirectory;
  </code></pre>
  
  <p>It gives me the error: `Unexpected keyword 'new' in the Object expression. Expected 'member', 'override' or other token.</p>
  
  <p>If I use <code>member</code>, the property <code>TemplateDirectory</code> gives this error:</p>
  
  <p><code>This instance member needs a parameter to represent the object being invoked. Make the member static or use the notation 'member x.Member(args) = ...'</code></p>