These classes provide implicit assignment operator ``operator=`` (for ``set``) and an implicit conversion operator ``operator T`` (for ``get``) to support items retrieved from the underlying Lua implementation, specifically :doc:`sol::table<table>` and the results of function calls on :doc:`sol::function<function>` and :doc:`sol::protected_function<protected_function>`.
``proxy`` is returned by lookups into :doc:`sol::table<table>` and table-like entities. Because it is templated on key and table type, it would be hard to spell: you can capture it using the word ``auto`` if you feel like you need to carry it around for some reason before using it. ``proxy`` evaluates its arguments lazily, when you finally call ``get`` or ``set`` on it. Here are some examples given the following lua script.
..code-block:: lua
:linenos:
:caption: lua nested table script
bark = {
woof = {
[2] = "arf!"
}
}
After loading that file in or putting it in a string and reading the string directly in lua (see :doc:`state`), you can start kicking around with it in C++ like so:
..code-block:: c++
:linenos:
sol::state lua;
// produces proxy, implicitly converts to std::string, quietly destroys proxy
We don't recommend the above to be used across classes or between function: it's more of something you can do to save a reference to a value you like, call a script or run a lua function, and then get it afterwards. You can also set functions (and function objects) this way, and retrieve them as well.
Gets the value associated with the keys the proxy was generated and convers it to the type ``T``. Note that this function will always return ``T&``, a non-const reference, to types which are not based on :doc:`sol::reference<reference>` and not a :doc:`primitive lua type<types>`
Returns whether this proxy actually refers to a valid object. It uses :ref:`sol::stack::probe_get_field<stack-probe-get-field>` to determine whether or not its valid.
Sets the value associated with the keys the proxy was generated with to ``value``. If this is a function, calls ``set_function``. If it is not, just calls ``set``. Does not exist on :ref:`unsage_function_result<unsafe-function-result>` or :ref:`protected_function_result<protected-function-result>`.
Sets the value associated with the keys the proxy was generated with to a function ``fx``. Does not exist on :ref:`unsafe_function_result<unsafe-function-result>` or :ref:`protected_function_result<protected-function-result>`.
Sets the value associated with the keys the proxy was generated with to ``value``. Does not exist on :ref:`unsafe_function_result<unsafe-function-result>` or :ref:`protected_function_result<protected-function-result>`.
``sol::stack_proxy`` is what gets returned by :doc:`sol::variadic_args<variadic_args>` and other parts of the framework. It is similar to proxy, but is meant to alias a stack index and not a named variable.
``unsafe_function_result`` is a temporary-only, intermediate-only implicit conversion worker for when :doc:`function<function>` is called. It is *NOT* meant to be stored or captured with ``auto``. It provides fast access to the desired underlying value. It does not implement ``set`` / ``set_function`` / templated ``operator=``, as is present on :ref:`proxy<proxy>`.
This type does, however, allow access to multiple underlying values. Use ``result.get<Type>(index_offset)`` to retrieve an object of ``Type`` at an offset of ``index_offset`` in the results. Offset is 0 based. Not specifying an argument defaults the value to 0.
``unsafe_function_result`` also has ``begin()`` and ``end()`` functions that return (almost) "random-acess" iterators. These return a proxy type that can be implicitly converted to :ref:`stack_proxy<stack-proxy>`.
``protected_function_result`` is a nicer version of ``unsafe_function_result`` that can be used to detect errors. Its gives safe access to the desired underlying value. It does not implement ``set`` / ``set_function`` / templated ``operator=`` as is present on :ref:`proxy<proxy>`.
This type does, however, allow access to multiple underlying values. Use ``result.get<Type>(index_offset)`` to retrieve an object of ``Type`` at an offset of ``index_offset`` in the results. Offset is 0 based. Not specifying an argument defaults the value to 0.
``unsafe_function_result`` also has ``begin()`` and ``end()`` functions that return (almost) "random-acess" iterators. These return a proxy type that can be implicitly converted to :ref:`stack_proxy<stack-proxy>`.
As of recent versions of sol2 (2.18.2 and above), this is no longer an issue, as even bound classes will have any detectable function call operator automatically bound to the object, to allow this to work without having to use ``.set`` or ``.set_function``. The note here is kept for posterity and information for older versions.
When you use the ``lua["object"] = doge{};`` from above, keep in mind that Sol detects if this is a function *callable with any kind of arguments*. Since ``doge`` has overriden ``return_type operator()( argument_types... )`` on itself, it results in satisfying the ``requires`` constraint from above. This means that if you have a user-defined type you want to bind as a :doc:`userdata with usertype semantics<usertype>` with this syntax, it might get bound as a function and not as a user-defined type (d'oh!). use ``lua["object"].set(doge)`` directly to avoid this, or ``lua["object"].set_function(doge{})`` to perform this explicitly.
