Protocol Composition
Protocol inheritance is a powerful tool that lets you easily create a new protocol to add requirements to an existing protocol or set of protocols. Nevertheless, using protocol inheritance can potentially lead you to make poor decisions in creating your types.
In fact, that is exactly what has happened with TabularDataSource
when you made it inherit from CustomStringConvertible because you wanted to be able to print a description of the data source.
(In fairness, you did it because we told you to.)
There is no correlation between the requirements of CustomStringConvertible and TabularDataSource, making them a poor candidate for inheritance. In a moment you will see how you can accomplish the same results without conflating ...
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