``sol::policies`` is an advanced, low-level modification feature allowing you to take advantage of sol3's abstractions before applying your own stack-based modifications at the last moment. They cover the same functionality as `luabind's "return reference to" and "dependency"`_ types. A few pre-rolled policies are defined for your use:
|``sol::returns_self`` | ``sol::policies( some_function, sol::returns_self() )`` | - takes the argument at stack index 1 (``self`` in member function calls and lambdas that take a specific userdata first) and makes that to be the return value |
| | | - rather than creating a new userdata that references the same C++ memory, it copies the userdata, similar to writing ``obj2 = obj1`` just increases the reference count |
| | | - saves memory space on top of keeping original memory alive |
|``sol::returns_self_with<int...>`` | ``sol::policies( some_function, sol::returns_self_with<2, 3>() )`` | - same as above, with the caveat that the ``self`` is returned while also putting dependencies into the ``self`` |
|``sol::self_dependency`` | ``sol::policies( some_function, sol::self_dependency() );`` | - this makes the value returned by the bindable take a dependency on the ``self`` argument |
|``sol::stack_dependencies`` | ``sol::policies( some_function, sol::stack_dependencies( target_index, 2, 1, ... ) );`` | - whatever is at ``target_index`` on the stack is given a special "keep alive" table with the elements on the stack specified by the integer indices after ``target_index`` |
| custom | ``sol::policies( some_function, [](lua_State* L, int current_stack_return_count) -> int { ... } )``| - whatever you want, so long as it has the form ``int (lua_State*, int )`` |
