Re: [Boost-users] [variant] variant member function apply_visitor( visitor ) thread-safe?

8 Sep 2008

      AMDG

Ovanes Markarian wrote:
...
so you mean there are no VTable fakes inside as it is suggested by Andrei
and in fact an additional numeric type identifier is stored? Which type from
the type list is stored?
At the lowest level, boost::variant<std::string, int> (e.g.)
looks something like:

class variant {
    boost::aligned_storage<
        max(sizeof(std::string), sizeof(int)),
        lcm(alignment_of<std::string>::value, alignment_of<int>::value)> 
buffer_;
    int which_;
};

apply_visitor is implemented something to the effect of

switch(which_) {
    case 0: return(f(*static_cast<std::string*>(buffer_.address())));
    case 1: return(f(*static_cast<int*>(buffer_.address())));
}

In Christ,
Steven Watanabe