Implement '*'-operator for classes with fixed code

Question

I have two C++-classes A and B that I can't change for various reasons. However, I'd like to be able to define a multiplication a*a and a*a. (Think of A as a rotation matrix and b as a vector). I of course could define a mult(const A& a, const B& b) but that gets unreadable if I have expressions like a*a'*b.

Is there a way to overload the *-operator for these classes without changing their code?

(If this is not possible, was there ever a discussion to add this feature to the language?)

A and B are autogenerated and I don't want to maintain changes in the generator. — FooTheBar, Feb 09 '16 at 18:44
See http://stackoverflow.com/questions/4421706/operator-overloading — juanchopanza, Feb 09 '16 at 18:45
@LogicStuff: thanks, that's what I wanted to do, know I know what to google. — FooTheBar, Feb 09 '16 at 18:48

score 2 · Accepted Answer · answered Feb 09 '16 at 18:46

2

You can define a global operator*() function exactly like you would do mult():

const B& operator*(const A& a, const B& b) {
    // code goes here
}

answered Feb 09 '16 at 18:46

Code-Apprentice

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NathanOliver · Answer 2 · 2016-02-09T19:09:20.877

2

If you cannot change the classes at all you can still write a global operator* like

B operator*(const A& a, const B& b)

But you will not be able to modify any of the private members of the classes unless the classes provide accessers to them

edited Feb 09 '16 at 19:09

answered Feb 09 '16 at 18:50

NathanOliver

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Implement '*'-operator for classes with fixed code

2 Answers2