[CMake] PARENT_SCOPE for unset()?

[Robert Dailey]

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
>>>>>>
>>>>>> Visit other Kitware open-source projects at
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>>>>>>
>>>>>> Please keep messages on-topic and check the CMake FAQ at:
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>>>>>>
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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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