[CMake] Hard to do if in Macro

[Petr Kmoch]

When returning values from a function, you have to use the PARENT_SCOPE
argument of set():

function( test __ANDROID__ RETVAL )

  if( ${__ANDROID__} EQUAL 1 OR ${__ANDROID__} STREQUAL "ON")
    set( ${RETVAL} ${${RETVAL}} qwer2 PASRENT_SCOPE)
    message( "Included..... " )
  endif( ${__ANDROID__} EQUAL 1 OR ${__ANDROID__} STREQUAL "ON")

  if( __ANDROID__ )
    set( ${RETVAL} ${${RETVAL}} asdf PARENT_SCOPE)
    message( "ALWAYS Included ${__ANDROID__}" )
  endif( __ANDROID__ )

endfunction( test )

Petr


On 30 January 2018 at 17:07, J Decker <d3ck0r at gmail.com> wrote:

> Okay... but then with function I can't set external variables; but if(
> __ANDROID__ ) works.
>
> `result` never changes.
>
> ---------------------------
>
> set( __ANDROID__ 1 )
>
> function( test __ANDROID__ RETVAL )
>
>   if( ${__ANDROID__} EQUAL 1 OR ${__ANDROID__} STREQUAL "ON")
>     set( ${RETVAL} ${${RETVAL}} qwer2 )
>     message( "Included..... " )
>   endif( ${__ANDROID__} EQUAL 1 OR ${__ANDROID__} STREQUAL "ON")
>
>   if( __ANDROID__ )
>     set( ${RETVAL} ${${RETVAL}} asdf )
>     message( "ALWAYS Included ${__ANDROID__}" )
>   endif( __ANDROID__ )
>
> endfunction( test )
>
>
> set( result "default" )
>
> test( __ANDROID__ "result" )
> message( "REsult:${result}" )
>
> test( ${__ANDROID__} "result" )
> message( "REsult:${result}" )
>
> test( OFF  "result")
> message( "REsult:${result}" )
>
> ---------------------------
>
>
>
>
> On Tue, Jan 30, 2018 at 12:35 AM, Petr Kmoch <petr.kmoch at gmail.com> wrote:
>
>> Macros aren't functions, and macro parameters aren't CMake variables.
>> Expanding a macro parameter is effectively *textual* substitution, whereas
>> dereferencing a CMake variable is a semantic one.
>>
>> In other words, inside your macro, the text __ANDROID__ (when not
>> expanded) never refers to the macro parameter. Macro parameters "don't
>> exist" outside of expansion context. The `if(__ANDROID__)` bit therefore
>> always refers to the variable __ANDROID__, never to the macro parameter
>> __ANDROID__.
>>
>> You still don't have to spell out the conditional as explicitly as you're
>> doing it now, but you have to expand the parameter:
>>
>> macro(test __ANDROID__)
>>   if(${__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
>>>
>>> --
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>
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