Editing Binary flags (section)

=== Unsetting Bitflags ===

The last thing we need to cover is how to unset bitflags. I mentioned that anything & 0 = 0, so you can be sure we'll use this.

The problem however is that the values we have (disabilities as 0b0110, DISABILITY_EYE, _EAR, _ARM, _LEG) are not really sufficient, since, if we just do a simple & between the disabilities variable and the constant for the disability, it will end up resetting everything else:

disabilities = disabilities & DISABILITY_EAR

disabilities = 0b0110 & 0b0010

disabilities = 0b0010

This is not what we want. We want the disability we add in to be reset. So we'll need a 0 in place of the disability flag, and a 1 everywhere else. This is because 1 AND anything = anything; at the same time anything AND 0 = 0.

So what we have to do is invert the DISABILITY_EAR constant. We do this with the NOT operator:

  /mob/proc/remove_disability(var/dis)
    disabilities = disabilities & ~dis

So now when we call remove_disability(DISABILITY_EAR) we will get

disabilities = disabilities & ~dis

disabilities = 0b0110 & ~0b0010

disabilities = 0b0110 & 0b1101

disabilities = 0b0100

In other words, disabilities will now no longer have the DISABILITY_EAR flag set.