# CMP0012

`if()` recognizes numbers and boolean constants.

In CMake versions 2.6.4 and lower the `if()` command implicitly dereferenced arguments corresponding to variables, even those named like numbers or boolean constants, except for `0` and `1`. Numbers and boolean constants such as `true`, `false`, `yes`, `no`, `on`, `off`, `y`, `n`, `notfound`, `ignore` (all case insensitive) were recognized in some cases but not all. For example, the code `if(TRUE)` might have evaluated as `false`. Numbers such as 2 were recognized only in boolean expressions like `if(NOT 2)` (leading to `false`) but not as a single-argument like `if(2)` (also leading to `false`). Later versions of CMake prefer to treat numbers and boolean constants literally, so they should not be used as variable names.

The `OLD` behavior for this policy is to implicitly dereference variables named like numbers and boolean constants. The `NEW` behavior for this policy is to recognize numbers and boolean constants without dereferencing variables with such names.

This policy was introduced in CMake version 2.8.0. CMake version 3.15.0-rc3 warns when the policy is not set and uses `OLD` behavior. Use the `cmake_policy()` command to set it to `OLD` or `NEW` explicitly.

Note

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