1function
2--------
3
4Start recording a function for later invocation as a command.
5
6.. code-block:: cmake
7
8  function(<name> [<arg1> ...])
9    <commands>
10  endfunction()
11
12Defines a function named ``<name>`` that takes arguments named
13``<arg1>``, ...  The ``<commands>`` in the function definition
14are recorded; they are not executed until the function is invoked.
15
16Per legacy, the :command:`endfunction` command admits an optional
17``<name>`` argument. If used, it must be a verbatim repeat of the
18argument of the opening ``function`` command.
19
20A function opens a new scope: see :command:`set(var PARENT_SCOPE)` for
21details.
22
23See the :command:`cmake_policy()` command documentation for the behavior
24of policies inside functions.
25
26See the :command:`macro()` command documentation for differences
27between CMake functions and macros.
28
29Invocation
30^^^^^^^^^^
31
32The function invocation is case-insensitive. A function defined as
33
34.. code-block:: cmake
35
36  function(foo)
37    <commands>
38  endfunction()
39
40can be invoked through any of
41
42.. code-block:: cmake
43
44  foo()
45  Foo()
46  FOO()
47  cmake_language(CALL foo)
48
49and so on. However, it is strongly recommended to stay with the
50case chosen in the function definition. Typically functions use
51all-lowercase names.
52
53.. versionadded:: 3.18
54  The :command:`cmake_language(CALL ...)` command can also be used to
55  invoke the function.
56
57Arguments
58^^^^^^^^^
59
60When the function is invoked, the recorded ``<commands>`` are first
61modified by replacing formal parameters (``${arg1}``, ...) with the
62arguments passed, and then invoked as normal commands.
63
64In addition to referencing the formal parameters you can reference the
65``ARGC`` variable which will be set to the number of arguments passed
66into the function as well as ``ARGV0``, ``ARGV1``, ``ARGV2``, ...  which
67will have the actual values of the arguments passed in.  This facilitates
68creating functions with optional arguments.
69
70Furthermore, ``ARGV`` holds the list of all arguments given to the
71function and ``ARGN`` holds the list of arguments past the last expected
72argument.  Referencing to ``ARGV#`` arguments beyond ``ARGC`` have
73undefined behavior.  Checking that ``ARGC`` is greater than ``#`` is
74the only way to ensure that ``ARGV#`` was passed to the function as an
75extra argument.
76