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> It's non-POD. For a stricter definition of POD which requires that byte-by-byte copies are possible. More informally, it's a POD because it only defines memb

> It's non-POD. For a stricter definition of POD which requires that byte-by-byte copies are possible. More informally, it's a POD because it only defines members and all the constructors and destructors are implicitly generated.

flohofwoe 2y ago
I've never seen this definition of 'POD' tbh, 'Plain Old Data' kinda implies that it behaves the same as a C struct when copying and destructing (e.g. the compiler is able to use a memcpy for copying, and destruction is a no-op - both is not the case when there's an embedded std::string object).
mort96 2y ago
I haven't heard your personal informal definition of POD before. I've only concerned myself with the standard's definition of POD. If you were using a different definition of POD than the standard, you should have specified that. Or better yet, not used the term "POD", since it is widely understood to mean what the standard refers to as "POD". EDIT: It seems I've had a slightly incorrect impression of "POD": what makes 'Person' non-POD isn't that it has an implicitly defined constructor but simply that it contains a non-POD type. The requirements for POD classes[1] includes "has no non-static data members of type non-POD class (or array of such types)". std::string is certainly a non-POD class, which makes discussion about Person's constructors and destructors moot. Not that it changes anything, but I don't wanna spread misinformation. [1] https://en.cppreference.com/w/cpp/language/classes#POD_class https://en.cppreference.com/w/cpp/language/classes#POD_class
gpderetta 2y ago
you are probably confusing POD with aggregate.
jcranmer 2y ago
The historical notion of POD is that it's a class type that has no C++ shenanigans going on, and thus works like it does in C. As a result, while there are a few slightly different definitions of POD, all of them share the commonality that having a non-POD member makes the class non-POD; in other words, POD-ness has a recursive quality. It doesn't make a lot of sense to not have this recursive quality to POD-ness, because the fact that C++ shenanigans are involved doesn't go away just because it's implicitly handled for you by the compiler.
elteto 2y ago
POD means you can memcpy without incurring undefined behavior, same as you would in C to copy a struct.

flohofwoe 2y ago

I've never seen this definition of 'POD' tbh, 'Plain Old Data' kinda implies that it behaves the same as a C struct when copying and destructing (e.g. the compiler is able to use a memcpy for copying, and destruction is a no-op - both is not the case when there's an embedded std::string object).

mort96 2y ago

I haven't heard your personal informal definition of POD before. I've only concerned myself with the standard's definition of POD. If you were using a different definition of POD than the standard, you should have specified that. Or better yet, not used the term "POD", since it is widely understood to mean what the standard refers to as "POD". EDIT: It seems I've had a slightly incorrect impression of "POD": what makes 'Person' non-POD isn't that it has an implicitly defined constructor but simply that it contains a non-POD type. The requirements for POD classes[1] includes "has no non-static data members of type non-POD class (or array of such types)". std::string is certainly a non-POD class, which makes discussion about Person's constructors and destructors moot. Not that it changes anything, but I don't wanna spread misinformation. [1] https://en.cppreference.com/w/cpp/language/classes#POD_class https://en.cppreference.com/w/cpp/language/classes#POD_class

gpderetta 2y ago

you are probably confusing POD with aggregate.

jcranmer 2y ago

The historical notion of POD is that it's a class type that has no C++ shenanigans going on, and thus works like it does in C. As a result, while there are a few slightly different definitions of POD, all of them share the commonality that having a non-POD member makes the class non-POD; in other words, POD-ness has a recursive quality. It doesn't make a lot of sense to not have this recursive quality to POD-ness, because the fact that C++ shenanigans are involved doesn't go away just because it's implicitly handled for you by the compiler.

elteto 2y ago

POD means you can memcpy without incurring undefined behavior, same as you would in C to copy a struct.