Hi
what's wrong about the following code? It does not compile.
template <typename T>
class A {
public:
class B;
};
template <typename T>
bool
operator==(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs);
template <typename T>
bool
operator!=(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs);
template <typename T>
class A<T>::B
{
public:
friend bool
operator==<>(co nst B &lhs, const B &rhs);
friend bool
operator!=<>(co nst B &lhs, const B &rhs);
};
template <typename T>
bool
operator==(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs)
{
return true;
}
template <typename T>
bool
operator!=(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs)
{
return false;
}
int
main()
{
A<int>::B b;
b == b;
}
regards,
Alex 1 2818
"Alexander Stippler" <st**@mathemati k.uni-ulm.de> wrote... what's wrong about the following code? It does not compile.
Several things are wrong. However, I'd like to know what prevented
you from posting the compiler diagnostic? template <typename T> class A { public: class B; };
template <typename T> bool operator==(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs);
template <typename T> bool operator!=(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs);
template <typename T> class A<T>::B { public: friend bool operator==<>(co nst B &lhs, const B &rhs);
If you need a particular instantiation to be a friend, you expect that
'T' is going to be determined here. It won't. The language does not
allow template argument deduction from nested types in templates. You
have to specify the T:
friend bool operator==<T>(. ..
.. friend bool operator!=<>(co nst B &lhs, const B &rhs);
Same here.
};
template <typename T> bool operator==(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs) { return true; }
template <typename T> bool operator!=(cons t typename A<T>::B &lhs, const typename A<T>::B &rhs) { return false; }
int main() { A<int>::B b; b == b;
Now, this is not going to be resolved. Again, because the compiler
does not know how to deduce type arguments from nested types, you
need to help it:
operator==<int> (b,b);
Ugly? Yes. But there is no other way. Perhaps you need to think
of making your operator== and operator!= templates based on B and
not on T:
template<typena me B> bool operator==(B const&, B const&);
and then specialise them for A<T>::B if needed... }
regards, Alex This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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