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Comment by dilap | Hacker News Reader

i haven't done c++ in a million years, but huh, you can! can't have any types w/ non-trival copy constructors in a union, though, apparently, which is quite the restriction.

https://gist.github.com/erinok/c823af95db408653c7e42ab189307...

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> can't have any types w/ non-trival copy constructors in a union, though, apparently, which is quite the restriction.

That was removed in C++11. The rule now is:

> Absent default member initializers ([class.mem]), if any non-static data member of a union has a non-trivial default constructor ([class.default.ctor]), copy constructor, move constructor ([class.copy.ctor]), copy assignment operator, move assignment operator ([class.copy.assign]), or destructor ([class.dtor]), the corresponding member function of the union must be user-provided or it will be implicitly deleted ([dcl.fct.def.delete]) for the union.

i.e., you need to provide an explicit version of the special function for the union if any member has a nontrivial implementation.

ah, good to know, thanks! unfortunately too late to edit my comment

You can have non trivial types in an union, but you need to explicitly define constructor in the union or the containing type (i.e. the default union copy constructor and assignment operator are disabled).

I may be wrong, but I thought it’s that you can’t have any fields with non trivial destructors, because the union wouldn’t know which destructor to call. So POD types / raw pointers / arrays of the above / structs of the above are allowed, and that’s pretty much it.

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