fork download

template<typename Derived>
struct Op
{
	template<typename ScalarType>
	friend Derived operator* (ScalarType const& Lambda, Derived Rhs)
	{
		return Rhs *= Lambda;
	}
};
 
template<typename T>
struct Foo
{
};
 
template<typename T>
struct Bar : Op<Bar<T> >
{
	template<typename U>
	Bar operator*= (U)
	{
		return *this;
	}
};
 
template<typename T>
void operator* (Foo<T>, Bar<T>)
{
}
 
int main()
{
	Foo<int>() * Bar<int>();
}

prog.cpp: In function ‘int main()’:
prog.cpp:33:13: error: ambiguous overload for ‘operator*’ (operand types are ‘Foo<int>’ and ‘Bar<int>’)
  Foo<int>() * Bar<int>();
             ^
prog.cpp:33:13: note: candidates are:
prog.cpp:27:6: note: void operator*(Foo<T>, Bar<T>) [with T = int]
 void operator* (Foo<T>, Bar<T>)
      ^
prog.cpp:5:17: note: Derived operator*(const ScalarType&, Derived) [with ScalarType = Foo<int>; Derived = Bar<int>]
  friend Derived operator* (ScalarType const& Lambda, Derived Rhs)
                 ^

Standard output is empty