Boost.Hana  1.5.0 Your standard library for metaprogramming
Enables ADL in the hana::detail::operators namespace.
This is used by containers in Hana as a quick way to automatically define the operators associated to some concepts, in conjunction with the detail::xxx_operators family of metafunctions.
Note that adl can be passed template arguments to make it unique amongst a set of derived classes. This allows a set of derived classes not to possess a common base class, which would disable the EBO when many of these derived classes are stored in a Hana container. If EBO is not a concern, adl<> can simply be used.