operator overriding

[dvm1]

Hello,

I need to create a class CASQLRow which overrides operator[]. The problem is the return value which might be different because of the sql field type.

What I did so far is:

class CASQLRow
{
public:
	virtual ~CASQLRow(){}
	virtual const char* operator[] (const char* field) const = 0;
	virtual const char* operator[] (int field) const = 0;
};

Yet, I would like something more like:

class CABlob;

class CASQLRow
{
public:
	virtual ~CASQLRow(){}
	virtual const char* operator[] (const char* field) const = 0;
	virtual const char* operator[] (int field) const = 0;
	virtual long operator[] (const char* field) const = 0;
	virtual long operator[] (int field) const = 0;
	virtual double operator[] (const char* field) const = 0;
	virtual double operator[] (int field) const = 0;
	virtual const CABlob & operator[] (const char* field) const = 0;
	virtual const CABlob & operator[] (int field) const = 0;
};

I know I am a c++ rookie, so please feel free to throw anything at me (especially valid information).

Thanks.

[Denis]

Overloaded methods should be different by params, not by return type
So your class CASQLRow is incorrect.

[dvm1]

Thanks for the reply.

I know it is incorrect. I would likt to know how to do this using an operator. Else I will use functions like:

...
virtual int value(const char* field, long& v) const = 0;
virtual int value(const char* field, double& v) const = 0;
virtual int value(const char* field, CABlob** v) const = 0;
...

I would like to know if it is possible to have this kind of functionaly using operator[].

Thank you

[Denis]

template <typename T>
const T& operator[](const char* field) const;

But in this case this operator can't be virtual

[dvm1]

Thanx,

I found an interesting solution to my problem. Perhaps it will be usefull for others:

http://www.parashift.com/c++-faq-lite/templates.html (35.7)

[jsmith]

Ok, that's why Denis suggested, but I'm not seeing how that solution provides a palatable
solution, because the template only on return type sort of defeats the purpose of the
operator in the first place (the purpose being to provide a more natural, intuitive syntax).

[jsmith]

Other alternatives include:

1) return a boost::variant<>;
2) return a boost::any;
3) use your own type erasure class (http://www.cplusplus.com/forum/articles/18756/);
4) always return a string, and perform conversions where necessary.