[CMake] PARENT_SCOPE for unset()?

[Robert Dailey]

Also I wonder what happens if you do this:

set( var PARENT_SCOPE PARENT_SCOPE PARENT_SCOPE )

---------
Robert Dailey


On Fri, Feb 10, 2012 at 8:59 AM, Robert Dailey <rcdailey at gmail.com> wrote:

> I actually found that using the following worked the exact same for me:
>
> set( var "" PARENT_SCOPE )
>
> It passed the "NOT" test in my if condition:
>
> if( NOT var )
> ...
> endif()
>
> It might make more sense to require 2 parameters for set() (the variable
> name and its value). If setting to nothing, use a blank string. That way
> there is no ambiguity between PARENT_SCOPE and parameter 2.
>
> If people really want to unset the variable, I don't believe set() is the
> way... that's why unset() exists. Just my opinion. Only problem is, if you
> make this change, it isn't backward compatible and will probably break a
> lot of scripts. Looks like CMake is kind of boned here. Herb Sutter made a
> great point during GoingNative 2012 about how it's better to "not have a
> feature" than to misdesign it and be stuck supporting it forever. I think
> the latter part of the statement applies here :)
>
> This isn't a big deal though, just one of those "if we could change it,
> this would make more sense" kind of things.
>
> Big thanks for your help David, as usual.
>
> ---------
> Robert Dailey
>
>
>
> On Thu, Feb 9, 2012 at 6:19 PM, David Cole <david.cole at kitware.com> wrote:
>
>> Yes, PARENT_SCOPE must occur as the last argument. Each command has its
>> own code for processing its argument list. See Source/cmSetCommand.cxx for
>> details on this one.
>>
>> Interesting (not quite the right adjective?) side effect: it's difficult
>> to set a variable to the value "PARENT_SCOPE" because you have to do it
>> indirectly...
>>
>>
>> On Thu, Feb 9, 2012 at 7:12 PM, Robert Dailey <rcdailey at gmail.com> wrote:
>>
>>> That worked, thanks David.
>>>
>>> I guess CMake goes right-to-left for function parameters? I don't see
>>> how else it doesn't think PARENT_SCOPE is a value instead of an option.
>>>
>>>  ---------
>>> Robert Dailey
>>>
>>>
>>>
>>> On Thu, Feb 9, 2012 at 1:45 PM, David Cole <david.cole at kitware.com>wrote:
>>>
>>>> On Thu, Feb 9, 2012 at 2:41 PM, Robert Dailey <rcdailey at gmail.com>wrote:
>>>>
>>>>> I didn't try that because I thought it would actually treat
>>>>> PARENT_SCOPE as a string and add it to the variable. I did this instead:
>>>>>
>>>>> set( var "" PARENT_SCOPE )
>>>>>
>>>>
>>>> That leaves it set, with a value of the empty string, in the parent
>>>> scope. Give the one I sent a try.
>>>>
>>>>
>>>>
>>>>>
>>>>> ---------
>>>>> Robert Dailey
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Feb 9, 2012 at 1:26 PM, David Cole <david.cole at kitware.com>wrote:
>>>>>
>>>>>> On Thu, Feb 9, 2012 at 2:22 PM, Alexander Neundorf <
>>>>>> a.neundorf-work at gmx.net> wrote:
>>>>>>
>>>>>>> On Thursday 09 February 2012, Robert Dailey wrote:
>>>>>>> > It would seem useful to have a PARENT_SCOPE option for the unset()
>>>>>>> command,
>>>>>>> > just like its set() counterpart. Is there a particular reason why
>>>>>>> it does
>>>>>>> > not have it now?
>>>>>>>
>>>>>>> No, I think there is not particular reason.
>>>>>>>
>>>>>>> Alex
>>>>>>> --
>>>>>>>
>>>>>>> Powered by www.kitware.com
>>>>>>>
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>>>>>>>
>>>>>>
>>>>>>
>>>>>> Does:
>>>>>>
>>>>>>   set(var PARENT_SCOPE)
>>>>>>
>>>>>> have the intended effect?
>>>>>>
>>>>>> (If so, you could use that until such time as PARENT_SCOPE is added
>>>>>> to unset.)
>>>>>>
>>>>>>
>>>>>> --
>>>>>>
>>>>>> Powered by www.kitware.com
>>>>>>
>>>>>> Visit other Kitware open-source projects at
>>>>>> http://www.kitware.com/opensource/opensource.html
>>>>>>
>>>>>> Please keep messages on-topic and check the CMake FAQ at:
>>>>>> http://www.cmake.org/Wiki/CMake_FAQ
>>>>>>
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>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>
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