[Cmake] Resetting a variable

[John Biddiscombe]

> You can change a cache value with a SET(var value FORCE).   However,
> this is a dangerous feature.   The problem is that cache variables
> can be set by the user.    If a cmakelist file changes the value set
> by a user, it can no longer be set by the user.

This has annoyed me many times...how does one change a default value to =
a different default (without editing the Cmake Modules). If you FORCE =
it, then it keeps getting reset every time the user changes it. If you =
don't, then you haven't changed the default,=20

you need to set a flag for the first time you run and change the default =
using FORCE, then clear the flag (anmd CACHE it) and afterwards stop =
FORCEing. it's grotesque...

how about some kind of SET (variable FORCEONCE) ! is there an easy way =
of doing it (especially if you need to change lots of variables)

JB