CMP0124

New in version 3.21.

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:

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 cmake_policy() command to set it to OLD or NEW explicitly. Unlike many policies, CMake version 3.27.9 does not warn when the policy is not set and simply uses OLD behavior.

Note

The OLD behavior of a policy is deprecated by definition and may be removed in a future version of CMake.