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I'm looking into the new, relaxed POD definition in C++11 (section 9.7) A standard-layout class is a class that: has no non-static data members of type non-standard-layout class (or array of such types) or reference, has no virtual functions (10.3) and no virtual base classes (10.1), has the same access control (Clause 11) for all non-static data members, has no non-standard-layout base classes, either has no non-static data members in the most derived class and at most one base class with non-static data members , or has no base classes with non-static data members, and has no base classes of the same type as the ﬁrst non-static data member . I've highlighted the bits that surprised me. What would go wrong if we tolerated data members with varying access controls? What would go wrong if the first data member was also a base class? i.e. struct Foo {}; struct Good : Foo {int x; Foo y;}; struct Bad : Foo {Foo y; int x;}; I admit it's a weird construction, but why should Bad be prohibited but not Good ? Finally, what would go wrong if more than one constituent class had data members?

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