On 11/14/2011 11:28 PM, Jonathan Wakely wrote:
On 14 November 2011 20:22, vagran.ast wrote:
Hi,
In the following code:
class A {
public:
void SomeMethod() { }
};
template<class T, void (T::*SomeMethod)() = 0>
class B {
};
B<A> b1; // error: could not convert template argument '0' to 'void
(A::*)()'
B<A, 0> b2; // error: could not convert template argument '0' to 'void
(A::*)()'
void (A::*someMethod)() = 0; // OK
there are two compilation errors. AFAIK per C++ standard 0 is a valid value
for a pointer to member
function. Variable of such type can be successfully initialized by 0 but
template arguments can not.
Is it desired behavior or a bug?
I think G++ is correct, you need to cast the literal zero to the right
type to prevent it being treated as an int in that context, or use
C++11's nullptr.
I have tried both variants and still no luck:
B<A, static_cast<void (A::*)()>(0)> b2;
// error: '((void (A::*)())0)' is not a valid template argument for type
'void (A::*)()'
// error: it must be a pointer-to-member of the form '&X::Y'
// error: could not convert template argument '((void (A::*)())0)' to
'void (A::*)()'
// error: invalid type in declaration before ';' token
B<A, nullptr> b3; // error: could not convert template argument
'nullptr' to 'void (A::*)()'
void (A::*someMethod)() = static_cast<void (A::*)()>(0);// OK
void (A::*someMethod2)() = nullptr;// OK
Seems the compiler wants only real method pointer for a template
parameter however
the conversion from NULL to member function pointer is possible.
