Initialize multiple constant class members using one function call C++

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In general, is there a way to do this without wasted function calls or memory?

Yes. This can be done with a delegating constructor, introduced in C++11.

A delegating constructor is a very efficient way to acquire temporary values needed for construction before any member variables are initialized.

int gcd(int a, int b); // Greatest Common Divisor

class Fraction {
public:
    // Call gcd ONCE, and forward the result to another constructor.
    Fraction(int a, int b) : Fraction(a,b,gcd(a,b))
    {
    }
private:
    // This constructor is private, as it is an
    // implementation detail and not part of the public interface.
    Fraction(int a, int b, int g_c_d) : numerator(a/g_c_d), denominator(b/g_c_d)
    {
    }
    const int numerator, denominator;
};

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