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Effective C++: discouraging protected inheritance?

Asked 2011-06-26T13:41:31.130
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I was reading Scott Meyers' Effective C++ (third edition), and in a paragraph in Item 32: Make sure public inheritance is "is-a" on page 151 he makes the comment (which I've put in bold):

This is true only for public inheritance. C++ will behave as I've described only if Student is publicly derived from Person. Private inheritance means something entirely different (see Item 39), and protected inheritance is something whose meaning eludes me to this day.

The question: how should I interpret this comment? Is Meyers trying to convey that protected inheritance is seldom considered useful and should be avoided?

(I've read the question Difference between private, public, and protected inheritance as well as C++ FAQ Lite's private and protected inheritance section, both of which explain what protected inheritance means, but hasn't given me much insight into when or why it would be useful.)

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Yes and no. I myself think that protected inheritance is a bad feature too. It basicly imports all the base class's public and protected members as protected members.

I usually avoid protected members, but on the lowest levels requiring extreme efficiency with a compiler with bad link-time optimization they are useful. But everything built on that shouldn't be messing with the original base class's (data) members and use the interface instead.

What I think Scott Meyer is trying to say, is that you can still use protected inheritance if it solves a problem, but make sure to use comments to describe the inheritance because it's not semantically clear.

answered 2011-06-26T13:53:54.177

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