This is an attempt to make boost::atomic<> interface closer to the standard. It
makes a difference in C++17 as it mandates copy elision, which makes this code
possible:
boost::atomic<int> a = 10;
It also makes is_convertible<T, boost::atomic<T>> return true, which has
implications on the standard library components, such as std::pair.
This removes the workaround for gcc 4.7, which complains that
operator=(value_arg_type) is considered ambiguous with operator=(atomic const&)
in assignment expressions, even though conversion to atomic<> is less preferred
than conversion to value_arg_type. We try to work around the problem from the
operator= side.
Added a new compile test to check that the initializing constructor is implicit.
1. Expose value_type and difference_type (where present) to user's code.
2. Prohibit arithmetic operations on pointers to non-object types. In
particular, arithmetic operations such as fetch_add/fetch_sub will no longer
compile for pointers to cv void, pointers to functions and pointers to
non-static class members.
Also, use C++11 <type_traits> when possible instead of Boost.TypeTraits to
reduce dependencies. Cleaned up value_arg_type internal type usage for more
efficient argument passing.
Platform selection now works in two stages. First compiler is tested for
the supported configuration. If that fails, OS is tested. Lastly, if
nothing succeeded, emulation backend is selected.
