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102 lines
3.9 KiB
ReStructuredText
102 lines
3.9 KiB
ReStructuredText
coroutine
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=========
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resumable/yielding functions from Lua
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-------------------------------------
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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 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 thread separate from your usual "main" :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()<status>` 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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.. code-block:: lua
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:caption: co.lua
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function loop()
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while counter ~= 30
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do
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coroutine.yield(counter);
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counter = counter + 1;
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end
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return counter
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end
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This is a function that yields:
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.. code-block:: cpp
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:caption: main.cpp
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sol::state lua;
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lua.open_libraries(sol::lib::base, sol::lib::coroutine);
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lua.script_file("co.lua");
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sol::coroutine cr = lua["loop"];
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for (int counter = 0; // start from 0
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counter < 10 && cr; // we want 10 values, and we only want to run if the coroutine "cr" is valid
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// Alternative: counter < 10 && cr.valid()
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++counter) {
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// Call the coroutine, does the computation and then suspends
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int value = cr();
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}
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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 = cr();``, then check ``result.valid()`` as is the case with :doc:`protected_function<protected_function>`. Finally, you can run this coroutine on another thread by doing the following:
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.. code-block:: cpp
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:caption: main_with_thread.cpp
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sol::state lua;
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lua.open_libraries(sol::lib::base, sol::lib::coroutine);
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lua.script_file("co.lua");
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sol::thread runner = sol::thread::create(lua.lua_state());
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sol::state_view runnerstate = runner.state();
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sol::coroutine cr = runnerstate["loop"];
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for (int counter = 0; counter < 10 && cr; ++counter) {
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// Call the coroutine, does the computation and then suspends
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int value = cr();
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}
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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: returning the coroutine's status
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:name: 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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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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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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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>`. |