Question

I’m trying to create an overridden operator function using both const parameters, but I can’t figure out how to do it. Here is a simple example:

class Number {     Number()     {         value = 1;     };      inline Number operator + (const Number& n)     {         Number result;          result.value = value + n.value;         return result;     }      int value; } 

What I am trying to do here is pass in two arguments into the addition function that are both const and return the result without changing anything in the class:

const Number a = Number(); const Number b = Number(); Number c = a + b; 

Is this possible and how would I go about doing this?

Thanks,

Dan

Answer 1

inline is understood in class declarations so you don’t need to specify it.

Most idiomatically, you would make operator+ a non-member function declared outside the class definition, like this:

Number operator+( const Number& left, const Number& right ); 

You might need to make it a friend of the class if it needs access to Number‘s internals.

If you have to have it as a member function then you need to make the function itself const:

Number operator+( const Number& n ) const { // ... 

For classes like Number, operator+ is typically implemented in terms of operator+= as usually you want all the usual operators to work as expected and operator+= is typically easier to implement and operator+ tends not to lose any efficiency over implementing it separately.

Inside the class:

Number& operator+=( const Number& n ); 

Outside the class:

Number operator+( const Number& left, const Number& right ) {     return Number( left ) += right; } 

or even:

Number operator+( Number left, const Number& right ) {     return left += right; }