Boost.Atomic 1.55 accepted structs with a user-defined default constructor as template argument, the version from the 1.56 test build doesn't (because of the union_cast). Is this by design? I could be wrong, but I thought the only requirement for structs to use them in atomics was that they were trivially coyable.
Yes, this is the property of the current implementation. The type has to be trivial (3.9/9). The previous versions compiled with types with non-trivial default constructors but the constructors were not actually called.
andrey, the standard requires that the type is trivially copyable, but it allows non-trivial constructors. this should be fixed for the 1.56 release, especially as it breaks existing code (including boost.lockfree). tim