Discussion on: Bitmasks: A very esoteric (and impractical) way of managing booleans

[Ben Sinclair]

Permissions are the only real way most people will see bitmasks these days unless you're doing something particularly low-level.
Like file permissions:

rwxr-xr-x

reads literally as

1111101101 (i.e. 755)

Not realising this is exactly why everyone abuses chmod -R 777 so wildly.

It's also good¹ for wrapping up complex permissions in a program:

function isLivingRelative(person) {
  return person.isAlive && person.isRelative;
}

function canBorrowMyCar(person) {
  return isLivingRelative(person) || person.wasQuickWithTheLawmowerThatOneTime;
}

vs.

const isAlive = 1;
const isRelative = 2;
const wasQuickWithTheLawmowerThatOneTime = 4;
const ISLIVINGRELATIVE = isAlive | isRelative;
const CANBORROWMYCAR = ISLIVINGRELATIVE | wasQuickWithTheLawmowerThatOneTime;

---

1. Meh, "good". ↩

[Basti Ortiz]

I was supposed to include an example on complex conditions in the article, but then I thought that it was probably getting too long already. Thanks for bringing this up!

Also, may I ask what the xs stand for in rwxr-xr-x?

[Ben Sinclair]

They're the execute bits - if it's a file, you can run it as a command, if it's a directory, you can cd into it.