Question

I have several types that share common behaviour and with same constructors and operators. Some look like this:

class NumberOfFingers
{
public:
    void operator=(int t) { this->value = t; }
    operator int() const { return this->value; }
private:
    int value;
};

NumberOfToes is identical.

Each class has different behaviour, here is an example:

std::ostream& operator<<(std::ostream &s, const NumberOfFingers &fingers)
{
    s << fingers << " fingers\n";
}

std::ostream& operator<<(std::ostream &s, const NumberOfFingers &toes)
{
    s << toes << " toes\n";
}

How can I minimise the duplication in the class definitions, whilst keeping class types distinct? I don’t want to have NumberOfFingers and NumberOfToes derive from a common base class because I lose the constructor and operators. I would guess a good answer would involve templates.

Answer 1

Yes, you are correct in that it would involve templates 🙂

enum {FINGERS, TOES...};
...
template<unsigned Type> //maybe template<enum Type> but I havent compiled this.
class NumberOfType
{
public:
    void operator=(int t) { this->value = t; }
    operator int() const { return this->value; }
private:
    int value;
};
...
typedef NumberOfType<FINGERS> NumberOfFinger
typedef NumberOfType<TOES> NumberOfToes
... so on and so forth.