4 ms·

The Linux shell command 'touch foo' is idempotent, but not side-effect free. Reading a variable shared between threads without a lock is side-effect free but n

by rcfox 5y ago

The Linux shell command 'touch foo' is idempotent, but not side-effect free. Reading a variable shared between threads without a lock is side-effect free but not idempotent.

omegalulw 5y ago
Reading a variable isn't side-effect free either :P
- zomglings 5y ago
  Opening Schrodinger's box isn't side-effect free. :)
- rcfox 5y ago
  In the sense that you're moving data in to a register and updating the program counter?
  - sokoloff 5y ago
    And potentially changing the contents of processor caches.
zomglings 5y ago
Interestingly, `touch` is not idempotent because it modifies timestamps. Not being pedantic, just an interesting consideration. `mkdir -p` is idempotent, I believe.
- mytailorisrich 5y ago
  You're absolutely correct, it's not idempotent for the crucial reason you mention. It's crucial because updating the timestamps is the main purpose of 'touch' in the first place!
- deleted 5y ago
  [deleted]