On 28/05/08 04:25 PM Beman Dawes wrote:
Neil Mayhew wrote:
... have a base class that contains everything except the constructors, and a derived class that adds the constructors
There are some issues with the base class approach. For it to be a POD, it can't have constructors, base classes, or private members.
Strictly speaking, yes, although we are only concerned about memory layout here, so the class doesn't have to be a true POD. The other concern is for the class to be able to live inside a union, and I think the constructors are the the only thing stopping that. (I #if'd the constructors and I was then able to use endian in a union.)
It might be better to just have two separate types, endian and old_endian. (old_endian isn't very clear as a name, but calling it pod_endian becomes invalid the moment C++0x ships.)
The typedefs to big32_t etc. would then be #if'd to correspond to the POD or non-POD classes as desired. I think this is better than putting the #if's around the constructors themselves.
Hummm... Seems too obscure. Better to have two sets of typedefs, with the C++03 set prefixed by old_ (or whatever better name anyone can come up with.)
I don't like "old_", at least not if it has to appear in my code! :-) I would like my client code to remain essentially the same when I upgrade to a C++0x compiler. This means having the same type names, which is why I suggested conditional typedefs. I thought this was cleaner than putting the conditionals inside the endian class itself. However, it doesn't make a lot of difference. Perhaps the simplest and best solution is therefore: class endian< ... > : cover_operators< ... > { public: #if defined(CXX_0X) || !defined(ENDIANS_IN_UNIONS) endian() {} endian(T val) { ... } #endif --Neil