Thorsten Ottosen skrev:
Hi Joaquin,
Sorry for the slow response.
Joaquin M Lopez Munoz skrev:
Thorsten Ottosen <nesotto <at> cs.aau.dk> writes:
Yep, why can't you just define null guard as
struct null_guard:boost::multi_index::detail::scope_guard_impl_base{};
Joaquin M Lopez Munoz skrev: the ?: operator seem to require that the second argument can be converted to the type of the first argument.
I might be missing something, but I think tou can simply write the following to circumvent the problem:
#define BOOST_AUTO_BUFFER_CONSTRUCTOR_SCOPE_GUARD() \ boost::has_nothrow_copy<T>::value ? \ static_cast<boost::multi_index::detail::scope_guard>( \ boost::auto_buffer_detail::null_guard()) : \ static_cast<boost::multi_index::detail::scope_guard>( \ boost::multi_index::detail::make_obj_guard( \ *this, \ &auto_buffer::deallocate, \ buffer_, members_.capacity_ ))
Does this work?
It seems to work.
I take that back. operator ?: seems to generate a redundant copy which kills this approach.
Additionally, why are you doing the guard selection on run time? boost::has_nothrow_copy<T>::value is a compile-time value so you can select the exact type of the guard (null or otherwise) with some Boost.MPL.
Well, I'm lazy, so I didn't want to implement the functionality twice with and without the guard. IMO the code is very clear with this macro. I think the optimizer has no problem removing the empty guard.
It seems to me that creating a null-guard conditioned on some compile-time value is quite common in containers that copy elements around. Would it not be possible to add a bool template parameter to make_obj_guard() such we can simply write scope_guard g = make_obj_guard<some_condition<T>::value>(...); ? -Thorsten