when defining a function which should be able to efficiently accept concatenated
strings.
-.. _function_apis:
-
-Passing functions and other callable objects
---------------------------------------------
-
-Sometimes you may want a function to be passed a callback object. In order to
-support lambda expressions and other function objects, you should not use the
-traditional C approach of taking a function pointer and an opaque cookie:
-
-.. code-block:: c++
-
- void takeCallback(bool (*Callback)(Function *, void *), void *Cookie);
-
-Instead, use one of the following approaches:
-
-Function template
-^^^^^^^^^^^^^^^^^
-
-If you don't mind putting the definition of your function into a header file,
-make it a function template that is templated on the callable type.
-
-.. code-block:: c++
-
- template<typename Callable>
- void takeCallback(Callable Callback) {
- Callback(1, 2, 3);
- }
-
-The ``function_ref`` class template
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-The ``function_ref``
-(`doxygen <http://llvm.org/doxygen/classllvm_1_1function_ref.html>`__) class
-template represents a reference to a callable object, templated over the type
-of the callable. This is a good choice for passing a callback to a function,
-if you don't need to hold onto the callback after the function returns.
-
-``function_ref<Ret(Param1, Param2, ...)>`` can be implicitly constructed from
-any callable object that can be called with arguments of type ``Param1``,
-``Param2``, ..., and returns a value that can be converted to type ``Ret``.
-For example:
-
-.. code-block:: c++
-
- void visitBasicBlocks(Function *F, function_ref<bool (BasicBlock*)> Callback) {
- for (BasicBlock &BB : *F)
- if (Callback(&BB))
- return;
- }
-
-can be called using:
-
-.. code-block:: c++
-
- visitBasicBlocks(F, [&](BasicBlock *BB) {
- if (process(BB))
- return isEmpty(BB);
- return false;
- });
-
-Note that a ``function_ref`` object contains pointers to external memory, so
-it is not generally safe to store an instance of the class (unless you know
-that the external storage will not be freed).
-``function_ref`` is small enough that it should always be passed by value.
-
-``std::function``
-^^^^^^^^^^^^^^^^^
-
-You cannot use ``std::function`` within LLVM code, because it is not supported
-by all our target toolchains.
-
-
.. _DEBUG:
The ``DEBUG()`` macro and ``-debug`` option