cmake/Help/policy/CMP0124.rst

CMP0124
-------

.. versionadded:: 3.21

:command:`foreach` loop variables are only available in the loop scope.

CMake 3.20 and below always leave the loop variable set at the end of the
loop, either to the value it had before the loop, if any, or to the empty
string.  CMake 3.21 and above prefer to leave the loop variable in the
state it had before the loop started, either set or unset.  This policy
provides compatibility for projects that expect the loop variable to always
be left set.

The ``OLD`` behavior for this policy is to set the loop variable at the
end of the loop, either to its original value, or to an empty value.
The ``NEW`` behavior for this policy is to restore the loop variable to
the state it had before the loop started, either set or unset.

For example:

.. code-block:: cmake

  set(items a b c)

  set(var1 "value")
  unset(var2)

  foreach(var1 IN LISTS items)
  endforeach()

  foreach(var2 IN LISTS items)
  endforeach()

  if(DEFINED var1)
    message("var1: ${var1}")
  endif()
  if(DEFINED var2)
    message("var2: ${var2}")
  endif()

Under the ``OLD`` behavior, this code prints ``var1: value`` and ``var2:``.
Under the ``NEW`` behavior, this code prints only ``var1: value``.

This policy was introduced in CMake version 3.21. Use the
:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
Unlike many policies, CMake version |release| does *not* warn when the policy
is not set and simply uses ``OLD`` behavior.

.. include:: DEPRECATED.txt