I was alluding to F#'s handling:

  > let myd = dict [ "a", 1; "the", 2; "train", 3 ];;
  val myd : System.Collections.Generic.IDictionary<string,int>

  > let myd = dict [ "a", System.String.IsNullOrEmpty ];;
  val myd : System.Collections.Generic.IDictionary<string,(string -> bool)>

If C# had tuples, then you might be able to do something like:

  var myd = createdict(new[] { {"a", 1} , { "the", 2} ...})

The tuples should get a type inferred, then the array, then that can pass the type to createdict and all good. And the array could be removed if there was some other sort of list-like literal. This might be really difficult to implement in the C# compiler, for all I know.

More likely, they'll graft in yet another special rule in the compiler (not accessible to user code!), just as they did with other collections, foreach, async, etc. I find it ugly that the compiler is happy to use static duck typing when convenient, but such a feature isn't exposed in the language.