On Monday 26 August 2024 12:59:54 GMT-7 Marc Mutz via Development wrote: > Part of why I'm sympathetic to the assertions throw mantra is that I > used it very successfully in Kleopatra way back when. We could easily > take the exception's what() and report back over the UI server channel > that an assertion happened and the client would show a message box with > the assertion details, copyable from a QMessageBox into a bugreport. > T'was a boon for testing.
Only developers would be interested in seeing exception names. Regular users
won't understand what that exception means and will just be confused.
I am also vehemently against catching exceptions you don't have a recovery
code path for. That destroys the stack trace and state that would have helped
the developer understand and actually fix the problem.
I suppose it's possible someone will use preconditions for recoverable
conditions, but I've never seen that even proposed, for any API. More
importantly, for the cases we have at hand, like:
static Qt::strong_ordering compareThreeWay_helper(const Iterator &lhs,
const Iterator &rhs)
noexcept
{
Q_ASSERT(lhs.item.d == rhs.item.d);
return Qt::compareThreeWay(lhs.item.i, rhs.item.i);
}
The most likely reason for violating this precondition is that the caller is
already corrupt and totally lost. I don't see how it could recover.
Another example is:
QUuid QCborValue::toUuid(const QUuid &defaultValue) const
{
if (!container || !isUuid() || container->elements.size() != 2)
return defaultValue;
Q_ASSERT(n == -1);
const ByteData *byteData = container->byteData(1);
if (!byteData)
return defaultValue; // UUIDs must always be 16 bytes, so this must be
invalid
return QUuid::fromRfc4122(byteData->asByteArrayView());
}
This is verifying an internal invariant state, not a precondition. The only
two reasons this assertion would trigger are a buggy implementation or
corrupted memory. Neither of which you can recover from with C++ code.
[This code isn't noexcept because QUuid::fromRfc4122 wasn't noexcept when it
was written]
--
Thiago Macieira - thiago.macieira (AT) intel.com
Principal Engineer - Intel DCAI Platform & System Engineering
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