[CMake] [PATCH] slightly modify cache variable behaviour, Was: Re: option() behavior

[Alexander Neundorf]

On Monday 11 May 2009, Bill Hoffman wrote:
> Alexander Neundorf wrote:
> > On Monday 11 May 2009, Bill Hoffman wrote:
> >> So, CMake has done what it does now from the start.   There was a short
> >> period of time when it did not, and that was when a re-write was done,
> >> and it quickly broke some existing projects.  Here is the thread:
> >
> > Yes, I can imagine that.
> > Still the current behaviour is not very intuitive, especially that
> > set(CACHE) in the first cmake run overrides the "visible" variable, while
> > the set(CACHE) in the second run basically does nothing, and so the value
> > of the "visible" variable is different.
> > I think for CMake 2.8 or 3.0 it would be a good idea to make this more
> > consistent and easier to understand (especially since now more and more
> > people are using cmake).
> >
> >> http://www.cmake.org/pipermail/cmake/2007-March/013204.html
> >>
> >> I think the rule should be if you want to change a variable you have to
> >> have the set AFTER the variable, or use CACHE INTERNAL.
> >
> > What do you mean exactly with "have the set after the variable" ?
> > Have the set(FOO <value>) after the set(FOO <value> CACHE), or something
> > else ?
>
> Yes,
>
> This always has worked as expected:
>
> set(FOO 2 CACHE)
> set(FOO 1)  # this is always the value
>
> However, I think your change is OK.  Basically if the set CACHE comes
> after the set, it will always set the value.   We do need a policy for
> this, but it should be easy to detected.  You will have to see if the
> REMOVE is going to do anything.    I wonder how many warnings that
> policy will cause... I  guess we could create the policy code, and try
> it on VTK, Boost, SecondLife, and some other big projects to see what
> happens...

Ok, I put it on my TODO, then we'll see what (would) happen.

Alex