[CMake] unset() command

[Fernando Cacciola]

Brad King wrote:
> Philip Lowman wrote:
>> On Wed, Aug 20, 2008 at 10:54 AM, Brad King <brad.king at kitware.com
>> <mailto:brad.king at kitware.com>> wrote:
>>
>>     The "set" command already supports unsetting:
>>
>>     set(FOO xyz)
>>     set(FOO) # unsets
>>     if(DEFINED FOO)
>>      message("This message does not appear.")
>>     endif(DEFINED FOO)
>>
>>     I think it should just be fixed for CACHE and ENV variables.
>>
>>
>> I knew that set() supported unsetting local variables but wasn't sure it
>> would be safe to extend it to CACHE and ENV variables as a bugfix. 
>> Regardless of whether this is appropriate to do or not adding an unset()
>> command also seemed to make the language simpler to understand because:
>>    set(FOO)
>> as someone else pointed out, is somewhat confusing.  Without referencing
>> the documentation many programmers might think this defines a variable
>> called FOO and sets it to empty but what it really is doing is
>> *undefining* the variable FOO entirely if it exists.
> 
> Okay, I agree.  It will be easier and more readable to add the unset
> command than to extend the "set" command to "unset" things :)
> 
> However, this:
> 
>   unset(MY_CACHE_VARIABLE)
> 
> should not remove the cache entry.  It should only unset the CMake
> variable.  In order to remove the cache entry, we should require
> 
>   unset(MY_CACHE_VARIABLE CACHE)
> 
> Otherwise there is no way to remove the variable without removing the
> cache entry.
> 
Makes sense.

And while you are it.. I currently use: set(var) to read the value
back from the cache (very usefull somtimes), but this is undocumented 
and extremely none-obvous, so, can we have a "fetch(var)" as well?

Should I formally suggest that via a bug report?


TIA

Fernando Cacciola