<programming> The traditional program comment for code
executed under a condition that should never be true, for
example a file size computed as negative. Often, such a
condition being true indicates data corruption or a faulty
algorithm; it is almost always handled by emitting a fatal
error message and terminating or crashing, since there is
little else that can be done.
Some case variant of "can't happen" is also often the text
emitted if the "impossible" error actually happens. Although
"can't happen" events are genuinely infrequent in production
code, programmers wise enough to check for them habitually are
often surprised at how frequently they are triggered during
development and how many headaches checking for them turns out
to head off.
See also firewall code, professional programming.
[Jargon File]
(1996-05-10)
Nearby terms:
canonical name « canonicity « C (ANSI) « can't happen » Cantor » CAP » Capabilities Maturity Model
