Question

Consider the following class:

class Test
{
public:
    Test( char );
    Test( int );
    operator const char*();
    int operator[]( unsigned int );
};

When I use it:

Test t;
Test& t2 = t[0];

I get a compiler error where it can’t figure out which operator[] to use. MSVC and Gcc both. Different errors. But same problem.

I know what is happening. It can construct a Test from either an int or a char, and it can either use Test::operator[] or it can cast to const char* and use the built char*[].

I’d like it to prefer Test::operator[].

Is there a way to specify a preference like this?

UPDATE: First, I’ll agree with response below that there is no language feature that lets you specify a priority for conversions. But like juanchopanza found below – you can create such a preference indirectly by making one conversion require no casts, and make the other require a cast. E.g. unsigned int as the argument for operator[] won’t work but, using int will.

The default index argument is unsigned – for gcc and msvc anyway – so making the index argument unsigned will cause the compiler to prefer the right operator.

@Konrad: about implicit conversions to built-in types. Agree generally. But I need it in this case.

Answer 1

No there isn’t. And this kind of ambiguity is why automatic conversions to another type (like operator char*) are not recommended.