Set a property on ViewBag dynamic object in F#

Question

I have this action method in C#:

  public ActionResult Index() {
      ViewBag.Message = \"Hello\";
      return View();
  }

And this

Answer 1

Instead of

x?ViewBag <- "Hello"

Try:

x.ViewBag?Message  <- "Hello"

Answer 2

Just to provide a similar example, the MvcMovie example in the ASP.NET Core docs uses the following controller method:

public IActionResult Welcome(string name, int numTimes = 1)
{
    ViewData["Message"] = "Hello " + name;
    ViewData["NumTimes"] = numTimes;

    return View();
}

converted to F#:

member this.Welcome (name : string, num_times : int) =
    this.ViewData.Add("Message", box ("Hello " + name))
    this.ViewData.Add("NumTimes", box num_times)

    this.View()    

Answer 3

The ViewBag property is just a wrapper that exposes the ViewData collection as a property of type dynamic, so that it can be accessed dynamically from C# (using property set syntax). You could use implementation of ? based on DLR to do that (see this discussion at SO), but it is easier to define ? operator that adds data directly to ViewDataDictionary (which is exposed by the ViewData property):

let (?<-) (viewData:ViewDataDictionary) (name:string) (value:'T) =
  viewData.Add(name, box value)

Then you should be able to write

x.ViewData?Message <- "Hello"