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da28527421
update large parts of the documentation and add a new section to streamline information about functions
88 lines
3.9 KiB
ReStructuredText
88 lines
3.9 KiB
ReStructuredText
function
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========
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calling functions bound to Lua
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------------------------------
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.. note::
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This abstraction assumes the function runs safely. If you expect your code to have errors (e.g., you don't always have explicit control over it or are trying to debug errors), please use :doc:`sol::protected_function<protected_function>` explicitly.
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.. code-block:: cpp
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class unsafe_function : public reference;
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typedef unsafe_function function;
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Function is a correct-assuming version of :doc:`protected_function<protected_function>`, omitting the need for typechecks and error handling (thus marginally increasing speed in some cases). It is the default function type of Sol. Grab a function directly off the stack using the constructor:
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.. code-block:: cpp
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:caption: constructor: function
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function(lua_State* L, int index = -1);
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When called without the return types being specified by either a ``sol::types<...>`` list or a ``call<Ret...>( ... )`` template type list, it generates a :ref:`function_result<function-result>` class that gets implicitly converted to the requested return type. For example:
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.. code-block:: lua
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:caption: func_barks.lua
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:linenos:
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bark_power = 11;
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function woof ( bark_energy )
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return (bark_energy * (bark_power / 4))
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end
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The following C++ code will call this function from this file and retrieve the return value:
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.. code-block:: cpp
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:linenos:
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sol::state lua;
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lua.script_file( "func_barks.lua" );
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sol::function woof = lua["woof"];
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double numwoof = woof(20);
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The call ``woof(20)`` generates a :ref:`function_result<function-result>`, which is then implicitly converted to an ``double`` after being called. The intermediate temporary ``function_result`` is then destructed, popping the Lua function call results off the Lua stack.
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You can also return multiple values by using ``std::tuple``, or if you need to bind them to pre-existing variables use ``sol::tie``:
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.. code-block:: cpp
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:linenos:
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sol::state lua;
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lua.script( "function f () return 10, 11, 12 end" );
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sol::function f = lua["f"];
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std::tuple<int, int, int> abc = f(); // 10, 11, 12 from Lua
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// or
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int a, b, c;
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sol::tie(a, b, c) = f(); // a = 10, b = 11, c = 12 from Lua
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This makes it much easier to work with multiple return values. Using ``std::tie`` from the C++ standard will result in dangling references or bad behavior because of the very poor way in which C++ tuples/``std::tie`` were specified and implemented: please use ``sol::tie( ... )`` instead to satisfy any multi-return needs.
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.. _function-result-warning:
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.. warning::
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Do NOT save the return type of a :ref:`function_result<function-result>` with ``auto``, as in ``auto numwoof = woof(20);``, and do NOT store it anywhere. Unlike its counterpart :ref:`protected_function_result<protected-function-result>`, ``function_result`` is NOT safe to store as it assumes that its return types are still at the top of the stack and when its destructor is called will pop the number of results the function was supposed to return off the top of the stack. If you mess with the Lua stack between saving ``function_result`` and it being destructed, you will be subject to an incredible number of surprising and hard-to-track bugs. Don't do it.
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.. code-block:: cpp
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:caption: function: call operator / function call
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template<typename... Args>
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function_result operator()( Args&&... args );
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template<typename... Ret, typename... Args>
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decltype(auto) call( Args&&... args );
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template<typename... Ret, typename... Args>
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decltype(auto) operator()( types<Ret...>, Args&&... args );
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Calls the function. The second ``operator()`` lets you specify the templated return types using the ``my_func(sol::types<int, std::string>, ...)`` syntax. Function assumes there are no runtime errors, and thusly will call the ``atpanic`` function if an error does occur.
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To know more about how function arguments are handled, see :ref:`this note<function-argument-handling>`
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