The documentation of QTimer::singleShot() states that the context/receiver should be a const pointer to QObject. This is consistent with e.g. QObject::connect().

However, in reality the overloads taking a functor require a non-const pointer, which is both inconvenient and against the documentation and standard practice.

Looking at qtimer.h, I see this:

// singleShot to a functor or function pointer (with context)
template <typename Duration, typename Func1>
static inline typename std::enable_if<!QtPrivate::FunctionPointer<Func1>::IsPointerToMemberFunction && !std::is_same<const char*, Func1>::value, void>::type
singleShot(Duration interval, QObject *context, Func1 slot)
{
    singleShot(interval, defaultTypeFor(interval), context, std::move(slot));
}

So this seems to be a bug in the method signature/implementation.