Question

Take for instance the SqlBulkCopy.WriteToServer() method. One of the overloads takes an IDataReader as the parameter. My question is, what’s the benefit/advantage to passing an interface to a method instead of the object instance itself?

http://msdn.microsoft.com/en-us/library/434atets.aspx

Answer 1

You can have many possible implementations for that one interface. Its better to depend on an abstraction (in this case an interface) than an actual concrete class – this allows much better flexibility and testability.

This also puts the focus on what is really required by the WriteToServer() method – the only thing its contract requires is for the caller to pass in any instance of a concrete class that provides the methods / properties declared by the IDataReader interface.