``table[x]`` and ``function(...)`` conversion struct
template <typename Recurring>
struct proxy_base;
template <typename Table, typename Key>
struct proxy : proxy_base<...>;
struct stack_proxy: proxy_base<...>;
struct unsafe_function_result : proxy_base<...>;
struct protected_function_result: proxy_base<...>;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:
.. literalinclude:: ../../../examples/source/table_proxy.cpp
:linenos:
:lines: 9-13
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:
.. literalinclude:: ../../../examples/source/table_proxy.cpp
:linenos:
:lines: 1-6,16-38
We don't recommend using proxy lazy evaluation 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:
.. literalinclude:: ../../../examples/source/table_proxy.cpp
:linenos:
:lines: 40-
requires( sol::is_primitive_type<T>::value == true )
template <typename T>
operator T() const;
requires( sol::is_primitive_type<T>::value == false )
template <typename T>
operator T&() const;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>`
template <typename T>
decltype(auto) get( ) const;Gets the value associated with the keys and converts it to the type T.
template <typename T, typename Otherwise>
optional<T> get_or( Otherwise&& otherise ) const;Gets the value associated with the keys and converts it to the type T. If it is not of the proper type, it will return a sol::nullopt instead.
template <typename T>
decltype(auto) get_or_create();
template <typename T, typename Otherwise>
decltype(auto) get_or_create( Otherwise&& other );Gets the value associated with the keys if it exists. If it does not, it will set it with the value and return the result.
bool valid () const;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.
requires( sol::detail::Function<Fx> == false )
template <typename T>
proxy& operator=( T&& value );
requires( sol::detail::Function<Fx> == true )
template <typename Fx>
proxy& operator=( Fx&& function );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>`.
template <typename Fx>
proxy& set_function( Fx&& fx );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>`.
template <typename T>
proxy& set( T&& value );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>`.
Note
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. There are only some small caveats, see: :ref:`this note here<binding-callable-objects>`.