[idea] Registration of user-provided mboxes as named ones

[eao197]

The current version of environment_t::create_mbox(name) always returns a mbox created by SObjectizer. It seems that we can provide a possibility to user to register own mbox as a named one.

Something like:

so_5::mbox_t custom_mbox = so_5::extra::mboxes::unique_subscribers::make(env);
env.register_named_mbox("my_mbox", custom_mbox);
...
auto mbox = env.create_mbox("my_mbox"); // the custom_mbox will be returned.

The changes to SObjectizer can look like:

namespace so_5
{

namespace named_mbox
{

enum class not_unique_name_reaction_t
{
  throw_exception,
  dont_throw_exception
};

constexpr auto throw_if_not_unique = not_unique_name_reaction_t::throw_exception;
constexpr auto nothrow_if_not_unique = not_unique_name_reaction_t::dont_throw_exception;

} /* namespace named_mbox */

class environment_t
{
public:
    ...
    // Returns false if name isn't unique and reaction is dont_throw_if_not_unique.
    bool
    register_named_mbox(nonempty_name_t mbox_name,
      named_mbox::not_unique_name_reaction_t reaction = named_mbox::throw_if_not_unique);
    ...
};

} /* namespace so_5 */

[eao197]

Implemented in v.5.8.0.