title: How can I overload the [] operators?
body: <p>I'm creating a class which populates a dictionary as a private member. I want to expose the values of the dictionary without exposing the dictionary itself (in a read-only fashion.) I can easily make a property to expose <code>_dictionary.Keys</code>, but how can I overload <code>[]</code> so that <code>MyClass[key]</code> returns <code>_dictionary[key]</code>?</p>
  
  <p>I think I may need to implement an interface, but I'm not sure which one...</p>