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authorAndy Belle-Isle <drumsetmonkey@gmail.com>2019-08-30 00:45:36 -0400
committerAndy Belle-Isle <drumsetmonkey@gmail.com>2019-08-30 00:45:36 -0400
commitdc2493e7525bb7633f697ef10f72b72b46222249 (patch)
tree9816755219e65d3f47fdce81c78f3736a7ddb8ab /lib/sol2/docs/source/tutorial/customization.rst
parent9d2b31797d0cfd130802b69261df2cd402e39b49 (diff)
Forget what I said, I just need to change git attributes to mark for vendor
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+adding your own types
+=====================
+
+Sometimes, overriding sol to make it handle certain ``struct``'s and ``class``'es as something other than just userdata is desirable. The way to do this is to take advantage of the 4 customization points for sol. These are ``sol_lua_check``, ``sol_lua_get``, ``sol_lua_push``, and ``sol_lua_check_get``.
+
+These are template class/structs, so you'll override them using a technique C++ calls *class/struct specialization*. Below is an example of a struct that gets broken apart into 2 pieces when going in the C++ --> Lua direction, and then pulled back into a struct when going in the Lua --> C++:
+
+.. literalinclude:: ../../../examples/source/customization_multiple.cpp
+ :name: customization-overriding
+ :caption: main.cpp
+ :linenos:
+ :lines: 1-52
+
+This is the base formula that you can follow to extend to your own classes. Using it in the rest of the library should then be seamless:
+
+.. literalinclude:: ../../../examples/source/customization_multiple.cpp
+ :name: customization-overriding-use
+ :caption: main.cpp
+ :linenos:
+ :lines: 52-
+
+And that's it!
+
+A few things of note about the implementation: First, there's an auxiliary parameter of type :doc:`sol::stack::record<../api/stack>` for the getters and checkers. This keeps track of what the last complete operation performed. Since we retrieved 2 members, we use ``tracking.use(2);`` to indicate that we used 2 stack positions (one for ``bool``, one for ``int``). The second thing to note here is that we made sure to use the ``index`` parameter, and then proceeded to add 1 to it for the next one.
+
+You can make something pushable into Lua, but not get-able in the same way if you only specialize one part of the system. If you need to retrieve it (as a return using one or multiple values from Lua), you should specialize the ``sol::stack::getter`` template class and the ``sol::stack::checker`` template class. If you need to push it into Lua at some point, then you'll want to specialize the ``sol::stack::pusher`` template class. The ``sol::lua_size`` template class trait needs to be specialized for both cases, unless it only pushes 1 item, in which case the default implementation will assume 1.
+
+.. note::
+
+ It is important to note here that the ``gett``, ``push`` and ``check`` differentiate between a type ``T`` and a pointer to a type ``T*``. This means that if you want to work purely with, say, a ``T*`` handle that does not have the same semantics as just ``T``, you may need to specify checkers/getters/pushers for both ``T*`` and ``T``. The checkers for ``T*`` forward to the checkers for ``T``, but the getter for ``T*`` does not forward to the getter for ``T`` (e.g., because of ``int*`` not being quite the same as ``int``).
+
+In general, this is fine since most getters/checkers only use 1 stack point. But, if you're doing more complex nested classes, it would be useful to use ``tracking.last`` to understand how many stack indices the last gett/check operation did and increment it by ``index + tracking.last`` after using a ``stack::check<..>( L, index, tracking)`` call.
+
+You can read more about the extension points themselves :ref:`over on the API page for stack<extension_points>`, and if there's something that goes wrong or you have anymore questions, please feel free to drop a line on the Github Issues page or send an e-mail!