[CMake] Hard to do if in Macro

[Petr Kmoch]

Macros aren't functions, and macro parameters aren't CMake variables.
Expanding a macro parameter is effectively *textual* substitution, whereas
dereferencing a CMake variable is a semantic one.

In other words, inside your macro, the text __ANDROID__ (when not expanded)
never refers to the macro parameter. Macro parameters "don't exist" outside
of expansion context. The `if(__ANDROID__)` bit therefore always refers to
the variable __ANDROID__, never to the macro parameter __ANDROID__.

You still don't have to spell out the conditional as explicitly as you're
doing it now, but you have to expand the parameter:

macro(test __ANDROID__)
  if(${__ANDROID__})
    message( "Included..... " )
  endif()
endmacro()

This is what the evaluation will look like based on how you call it:

test(__ANDROID__)   -> if(__ANDROID__) -> refers to the variable
set(__ANDROID__ 1)
test(${__ANDROID__})   -> if(1)
set(__ANDROID__ 0)
test(${__ANDROID__})   -> if(0)
test(OFF)   -> if(OFF)

CMake macros have a lot of specific and potentially weird/counterintuitive
behaviour. In general, you should always write your commands as functions
and only resort to macros if you explicitly need their specific behaviour.

Petr



On 30 January 2018 at 09:11, J Decker <d3ck0r at gmail.com> wrote:

> Why do I have to do
>
> if( ${M__ANDROID__} EQUAL 1 OR ${M__ANDROID__} STREQUAL "ON")
> endif( ${M__ANDROID__} EQUAL 1 OR ${M__ANDROID__} STREQUAL "ON")
>
> in a macro like...
> ----------------------
>
> set( __ANDROID__ 1 )
>
> macro( test __ANDROID__ )
>
>   if( ${__ANDROID__} EQUAL 1 OR ${__ANDROID__} STREQUAL "ON")
>     message( "Included..... " )
>   endif( ${__ANDROID__} EQUAL 1 OR ${__ANDROID__} STREQUAL "ON")
>
>   if( __ANDROID__ )
>     message( "ALWAYS Included ${__ANDROID__}" )
>   endif( __ANDROID__ )
>
> endmacro( test )
>
> test( __ANDROID__ )
> test( ${__ANDROID__} )
> test( OFF )
>
> ----------
> Output
>
> Included.....
> ALWAYS Included __ANDROID__
> Included.....
> ALWAYS Included 1
> ALWAYS Included OFF
>
> --
>
> Powered by www.kitware.com
>
> Please keep messages on-topic and check the CMake FAQ at:
> http://www.cmake.org/Wiki/CMake_FAQ
>
> Kitware offers various services to support the CMake community. For more
> information on each offering, please visit:
>
> CMake Support: http://cmake.org/cmake/help/support.html
> CMake Consulting: http://cmake.org/cmake/help/consulting.html
> CMake Training Courses: http://cmake.org/cmake/help/training.html
>
> Visit other Kitware open-source projects at http://www.kitware.com/
> opensource/opensource.html
>
> Follow this link to subscribe/unsubscribe:
> https://cmake.org/mailman/listinfo/cmake
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://cmake.org/pipermail/cmake/attachments/20180130/18db2dd3/attachment.html>