D171 - Out-parameters are always written

Status: decided Date: 2026-08-21

A function that answers through an out-pointer always writes it, with zero where the value is unknown, and reports success.

Why: an unwritten out-pointer leaves whatever the stack held, which differs from run to run and leaves no signature in a trace. Zero is an ordinary state a title must already handle - the first index, off, none - while any other value is a guess dressed as a default.

Rejected:

• Leaving the out-parameter unwritten: nondeterministic and unrecognisable.
• A plausible non-zero default: invented behaviour.