Calling another constructor when constructing an object with const members

Question

I have a class with const members, and one constructor which calls another constructor with extra values filled in. Normally I could use a colon initializer for

Answer 1

Where to put the results of myfunc so it can be set and used from different mem-initializers? How about in a default argument?

class A
{
private:
    struct InitData;
public:
    A(int b, InitData data=InitData());
    A(int b, int c, int d) : b(b), c(c), d(d) { };

    const int b;
    const int c;
    const int d;
};

struct A::InitData
{
    int setup(int b);
    int c;
    int d;
};

inline int A::InitData::setup(int b)
{
    myfunc(b, &c, &d);
    return b;
}

inline A::A(int b_, InitData data)
    : b(data.setup(b_)),
      c(data.c),
      d(data.d)  {}

A a(0);

Since the made up type is private and has no conversions, there's little risk of accidentally using it or abusing it.