https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80311
Bug ID: 80311
Summary: Bound member functions extension allows bogus
conversions
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
struct X {
int i = 0;
int f() { return i; }
};
int main() {
X x;
using fp = int (*)();
auto f = (fp)(&X::f);
return f();
}
This bogus attempt to use
https://gcc.gnu.org/onlinedocs/gcc/Bound-member-functions.html fails, because
there is no 'this' pointer provided for the call to the bound function.
G++ should notice this and give a diagnostic, even with -Wno-pmf-conversions.
The diagnostic should be given when converting to a function pointer that
doesn't match the arguments that would be needed for the bound function.
i.e. for (fp)(&X::f) or (fp)(x.*pmf) where that resovles to a pointer to:
R Y::f(Args...)
we should warn if fp is not R (*)(Y*, Args...).
This should simply be an error, not a warning. I see no reason to allow the
extension to form invalid function pointers. Code that really really wants to
do so can always perform a conversion after forming the bound function pointer:
struct X {
int i = 0;
int f() { return i; }
};
int main() {
X x;
using wrong_type = int(*)();
using right_type = int(*)(X*);
auto f = (wrong_type)(right_type)(&X::f);
return ((right_type)f)();
}
Maybe -fpermissive could cause it to be allowed without the extra conversion,
for legacy code misusing the feature.
