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function
--------
Start recording a function for later invocation as a command.
.. code-block:: cmake
function(<name> [<arg1> ...])
<commands>
endfunction()
Defines a function named ``<name>`` that takes arguments named
``<arg1>``, ... The ``<commands>`` in the function definition
are recorded; they are not executed until the function is invoked.
Per legacy, the :command:`endfunction` command admits an optional
``<name>`` argument. If used, it must be a verbatim repeat of the
argument of the opening ``function`` command.
A function opens a new scope: see :command:`set(var PARENT_SCOPE)` for
details.
See the :command:`cmake_policy()` command documentation for the behavior
of policies inside functions.
See the :command:`macro()` command documentation for differences
between CMake functions and macros.
Invocation
^^^^^^^^^^
The function invocation is case-insensitive. A function defined as
.. code-block:: cmake
function(foo)
<commands>
endfunction()
can be invoked through any of
.. code-block:: cmake
foo()
Foo()
FOO()
cmake_language(CALL foo)
and so on. However, it is strongly recommended to stay with the
case chosen in the function definition. Typically functions use
all-lowercase names.
.. versionadded:: 3.18
The :command:`cmake_language(CALL ...)` command can also be used to
invoke the function.
Arguments
^^^^^^^^^
When the function is invoked, the recorded ``<commands>`` are first
modified by replacing formal parameters (``${arg1}``, ...) with the
arguments passed, and then invoked as normal commands.
In addition to referencing the formal parameters you can reference the
``ARGC`` variable which will be set to the number of arguments passed
into the function as well as ``ARGV0``, ``ARGV1``, ``ARGV2``, ... which
will have the actual values of the arguments passed in. This facilitates
creating functions with optional arguments.
Furthermore, ``ARGV`` holds the list of all arguments given to the
function and ``ARGN`` holds the list of arguments past the last expected
argument. Referencing to ``ARGV#`` arguments beyond ``ARGC`` have
undefined behavior. Checking that ``ARGC`` is greater than ``#`` is
the only way to ensure that ``ARGV#`` was passed to the function as an
extra argument.
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