C ++多重继承-带模板的菱形

Question

I've got a problem when inheriting from multiple instances of a template.

My class Bridge tries to inherit from 2 instances of BridgeTemplate, so when we try to call the BridgeTemplate's 'set' function, the compiler rises an error ("ambiguous..."). However, everything works ok if Bridge inherits from only 1 instance.

Below, a piece of code from both the template and class Bridge. Thanks in advance

template <class DataType, class DataWriter>
class BridgeTemplate : public BridgeGeneric
{
    public:
        void set(DataType a, DataWriter b)
        {
            std::cout << "a: " << a << "; b: " << b << std::endl;
        }
...
};

class Bridge : public virtual BridgeTemplate<int,float>, public virtual BridgeTemplate<float,int>
{
...
}

Answer 1

Argument types do not matter.

The error message applies to name lookup, not to overload resolution. All overloaded functions must come from the same class or namespace. In order to insure that, use this pattern:

 class Child : public Dad, public Mom {
     using Dad::func;
     using Mom::func;
 };

 // ...

 Child c;
 c.foo(1, 2.3);

Because of the using declarations, both func members are brought to the Child namespace and the lookup is no longer ambiguous.