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
std::string x = lua["bark"]["woof"][2];
``proxy`` lazy evaluation:
..code-block:: c++
:linenos:
:caption: multi-get
auto x = lua["bark"];
auto y = x["woof"];
auto z = x[2];
// retrivies value inside of lua table above
std::string value = z; // "arf!"
// Can change the value later...
z = 20;
// Yay, lazy-evaluation!
int changed_value = z; // now it's 20!
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 :ref:`*<note 1>`) this way, and retrieve them as well.
..code-block:: c++
:linenos:
lua["bark_value"] = 24;
lua["chase_tail"] = floof::chase_tail; // chase_tail is a free function
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:`function_result<function-result>` or :ref:`protected_function_result<protected-function-result>`. See :ref:`note<note 1>` for caveats.
Sets the value associated with the keys the proxy was generated with to a function ``fx``. Does not exist on :ref:`function_result<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:`function_result<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.
``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>`.
``protected_function_result`` is a nicer version of ``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>`.
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.
