Item 33. Name Lookup and the Interface Principle—Part 3

Difficulty: 5

Take a few minutes to consider some implications of the Interface Principle on the way we reason about program design. We'll revisit a classic design problem: "What's the best way to write operator<<()?"

There are two main ways to write operator<<() for a class: as a free function that uses only the usual interface of the class (and possibly accessing nonpublic parts directly as a friend), or as a free function that calls a virtual Print() helper function in the class.

Which method is better? What are the tradeoffs?