https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115664
Bug ID: 115664
Summary: -Wnonnull-compare breaks templated methods
Product: gcc
Version: 13.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ossman at cendio dot se
Target Milestone: ---
A templated method has this protection in it to check that a given argument is
a subclass:
template<class T>
Object::method(void (*callback)(T*))
{
if (dynamic_cast<T*>(this) == nullptr)
throw Exception("Bad callback");
registerCallback(callback);
}
This works fine as long as T is a subclass of Object. However, if T is Object,
then the gcc is clever enough to realise that dynamic_cast<>() does nothing and
the comparison becomes just "if (this == nullptr)", which triggers
-Wnonnull-compare.
The problem is that this is a templated method, so that if statement is
sometimes useful and cannot be removed.
Presently, we have to work around the issue by having a specialised version of
the affected methods, which adds unnecessary duplication.
