Question

The function below returns a type of Dynamic, what is the most efficient way to cast it to IDictionary

 public dynamic GetEntities(string entityName, string entityField)

Answer 1

I’d probably go with the as operator.

var result = GetEntities("blah", "blahblah") as IDictionary<string,string>;

Then do a null check.

UPDATE

In regards to the “efficient” part of your question, I think as may be pretty efficient compared to some other paths you could take:

1. You could just blindly cast it to IDictionary<string,string> and
   then catch the exception, but using exceptions for control flow
   isn’t a good idea and is expensive.
2. You could use a convention like expression is type ? (type)expression : (type)null, but in this case, you evaluate
   expression twice (but you do get a null if the expected type isn’t
   the type that expression returns). So you’re doing double
   evaluations.
3. as is only good for reference or boxing conversions, not to perform user-defined conversions, so if you need that, then as
   isn’t for you.

See this article on MSDN.

UPDATE 2

I made an assumption on the key/value types of the IDictionary. You could just use IDictionary after as instead of specifying the generic type parameters. I guess it depends on what you’re expecting.

Hope this helps.