Do you agree that its support for member data initialization would be the main reason for having boost::initialized<T>?
Jeffrey Hellrung wrote:
Yes.
Within the context of member data initialization, the "explicit" keyword doesn't do anything. (For example, when the class has a data member of type boost::initialized<T>.) That's why I though the extra boost::direct_initialized_t tag parameter might be useful. Clearly so far I haven't convinced anyone. But I realize such a tag parameter will be less relevant when we're going to introduce a new initialized<T> template class, instead of modifying the interface of the old boost::value_initialized<T>. Fernando's boost::value_initialized<T> has been around for so long that I think backward-compatibility should be taken into account.
Is that MSVC bug (the one referenced in the value_initialized ticket...no link handy at the moment) not "workaroundable" by explicitly defining the derived class' copy constructor?
MSVC bug (reported independently by both srconchiwa and Edward Diener): http://connect.microsoft.com/VisualStudio/feedback/details/423737/default-co... http://connect.microsoft.com/VisualStudio/feedback/details/522094/warning-c4... value_initialized ticket by Edward: https://svn.boost.org/trac/boost/ticket/3472 (Yes, I added a reference to our discussion!)
And isn't it only a problem when the base class has a constructor other than the copy constructor that that a const derived& can bind to? Perhaps I need to go back and reread the Microsoft ticket...
Honestly the MSVC bug just made me more aware that copy-constructors and non-copy-constructors can get confused, in a generic context. But the example I added to the ticket (#3472) would also be ambiguous on other compilers, when value_initialized(T const&) would be added: class my_integer { value_initialized<int> m_data; public: operator value_initialized<int>() const; operator int() const; }; int main() { my_integer my; value_initialized<int> val(my); } See http://codepad.org/zukxSDbB Remaining question, triggered by the comments by Steven: should the new direct-initializing boost::initialized<T> constructor itself be a template? In that case, the "explicit" keyword certainly would make more sense to me: // Note: untested! template<class T> class initialized { ... public: initialized(); template<class U> explicit initialized(U const&); T const & data() const; T& data(); void swap(initialized &); operator T const &() const; operator T&(); }; What do you think? Kind regards, Niels -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center