93 lines
3.8 KiB
ReStructuredText
93 lines
3.8 KiB
ReStructuredText
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coroutine
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=========
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*resumable/yielding functions from Lua*
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A ``coroutine`` is a :doc:`reference<reference>` to a function in Lua that can be called multiple times to yield a specific result. It is a cooperative function. It is run on the :doc:`lua_State<state>` that was used to create it (see :doc:`thread<thread>` for an example on how to get a coroutine that runs on a stack space separate from your usual "main" stack space :doc:`lua_State<state>`).
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The ``coroutine`` object is entirely similar to the :doc:`protected_function<protected_function>` object, with additional member functions to check if a coroutine has yielded (:doc:`call_status::yielded<types>`) and is thus runnable again, whether it has completed (:ref:`call_status::ok<call-status>`) and thus cannot yield anymore values, or whether it has suffered an error (see :ref:`status()<thread-status>`'s and :ref:`call_status<call-status>`'s error codes).
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For example, you can work with a coroutine like this:
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.. literalinclude:: ../../../examples/source/docs/coroutine_main.cpp
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:caption: co.lua
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:name: co-lua
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:lines: 8-15
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:linenos:
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This is a function that yields. We set the ``counter`` value in C++, and then use the coroutine to get a few values:
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.. literalinclude:: ../../../examples/source/docs/coroutine_main.cpp
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:caption: coroutine_main.cpp
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:name: coroutine_main
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:lines: 1-6,18-19,21,25-
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:linenos:
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Note that this code doesn't check for errors: to do so, you can call the function and assign it as ``auto result = loop_coroutine();``, then check ``result.valid()`` as is the case with :doc:`protected_function<protected_function>`.
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Finally, you can run this coroutine on another stack space (NOT a different computer thread: Lua uses the term 'thread' a bit strangely, as we follow its usage of the term, but it is NOT a separate thread) by doing the following:
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.. literalinclude:: ../../../examples/source/docs/coroutine_thread.cpp
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:caption: coroutine_thread.cpp
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:name: yield-main-thread
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:lines: 1-6,18-19,21,25-
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:linenos:
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The following are the members of ``sol::coroutine``:
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members
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-------
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.. code-block:: cpp
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:caption: function: constructor
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:name: sol-coroutine-constructor
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coroutine(lua_State* L, int index = -1);
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Grabs the coroutine at the specified index given a ``lua_State*``.
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.. code-block:: cpp
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:caption: returning the coroutine's status
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:name: sol-coroutine-status
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call_status status() const noexcept;
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Returns the status of a coroutine.
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.. code-block:: cpp
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:caption: checks for an error
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:name: sol-coroutine-error
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bool error() const noexcept;
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Checks if an error occured when the coroutine was run.
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.. _runnable:
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.. code-block:: cpp
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:caption: runnable and explicit operator bool
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:name: sol-coroutine-runnable
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bool runnable () const noexcept;
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explicit operator bool() const noexcept;
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These functions allow you to check if a coroutine can still be called (has more values to yield and has not errored). If you have a coroutine object ``coroutine my_co = /*...*/``, you can either check ``runnable()`` or do ``if ( my_co ) { /* use coroutine */ }``.
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.. code-block:: cpp
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:caption: calling a coroutine
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:name: sol-coroutine-operator-call
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template<typename... Args>
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protected_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 coroutine. The second ``operator()`` lets you specify the templated return types using the ``my_co(sol::types<int, std::string>, ...)`` syntax. Check ``status()`` afterwards for more information about the success of the run or just check the coroutine object in an ifs tatement, as shown :ref:`above<runnable>`.
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