Template classes using each other gives ambiguity error - c++

Question

I have two template classes A and B in the same header file as follows:
template <typename T>
class FirstClass {
public:
bool convert(const FirstClass<T>& f){...}
bool convert(const SecondClass<T>& s){...}
};
template <typename T>
class SecondClass {
public:
bool convert(const FirstClass<T>& f){...}
bool convert(const SecondClass<T>& s){...}
};
In order to resolve any unknown class errors, I tried adding a forward declaration:
template <typename T> class SecondClass ; //adding this to the beginning of the file
I get the following error:
2 overloads have similar conversions
could be 'bool FirstClass<T>::convert(const FirstClass<T>& )'
or
could be 'bool FirstClass<T>::convert(const SecondClass<T>& )'
while trying to match the argument list '(FirstClass<T>)'
note: qualification adjustment (const/volatile) may be causing the ambiguity
I am assuming this is because I am using a forward declared class. Other than moving the implementation to Cpp files( which I have been told is cumbersome), is there any other efficient solution to this?
I am using VisualStudio 2010 on Windows 7

Answer 1

Just put the forward declarations before you define any of the two classes.
#include <iostream>
template<typename> class FirstClass;
template<typename> class SecondClass;
template <typename T>
class FirstClass {
public:
bool convert(const FirstClass<T>& f) { std::cout << "f2f\n"; }
bool convert(const SecondClass<T>& s){ std::cout << "f2s\n"; }
};
template <typename T>
class SecondClass {
public:
bool convert(const FirstClass<T>& f){ std::cout << "s2f\n"; }
bool convert(const SecondClass<T>& s){ std::cout << "s2s\n"; }
};
int main()
{
FirstClass<int> f;
SecondClass<int> s;
f.convert(f);
f.convert(s);
s.convert(f);
s.convert(s);
}
Output on Ideone