Is std::array guaranteed to be POD if T is POD?

Question

I\'m currently writing a C++ memory editing library and for the read/write APIs I use type traits (std::is_pod, std::is_same) and boost::enable_if to provide 3 overloads:

Answer 1

Potatoswatter found an error in my conclusions. C++ explicitly allows an implementation to explicitly define an assignment operator "with the same apparent semantics". This will make it a non-trivially copyable type. Making it community wiki...

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It seems to me you don't want to test against PODnes, but against trivially copyable, which is way less restricting. Because that is how C++0x constraints types that can be used with memcpy and friends.

And while I don't think there are any guarantees about PODness of std::array, there are guarantees about trivial copyability, as the following shows (if I haven't got an error in the conclusions). As we know std::array is an aggregate, and aggregates are

An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no brace-or-equal- initializers for non-static data members (9.2), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions (10.3).

While trivially copyability is defined for a class that has class that

• has no non-trivial copy constructors (12.8),
• has no non-trivial move constructors (12.8),
• has no non-trivial copy assignment operators (13.5.3, 12.8),
• has no non-trivial move assignment operators (13.5.3, 12.8), and
• has a trivial destructor (12.4).

std::array has no destructor (as a comment in the definition of std::array says). This does not seem to follow from the definition of aggregate classes though, even though the comment in std::array's class definition claims that.

The remaining 4 requirements follow from the absence of bases, virtual functions and user provided versions for those 4 special member functions for aggregates.