Kim Barrett wrote:
boost::throw_exception (in the interesting case, where BOOST_NO_EXCEPTIONS and BOOST_EXCEPTION_DISABLE are both undefined) ensures that the thrown object is derived from boost::exception even if the argument is not. It does this (via enable_error_info(), which does the heavy lifting) by examining the type E of the argument. If E is derived from boost::exception, then just use the argument as is. Otherwise, construct a new object. The class of the new object derives from both E and boost::exception (multiple inheritance), and has a conversion constructor for arguments of type E which passes the argument to the new class's base E object's copy constructor. Apply that constructor to the original argument, and use the resulting object. (Note that throw requires the argument to be copy constructible, so the described mechanism imposes no new constraint on E by requiring copy construction.)
So any boost library which previously used boost::throw exception with an exception which was non-copyable would break? I guess we're lucky no one did that. thanks for explaining this. I would never have figured it without spending a lot of time. Robert Ramey