Non-const copy constructor and implicit conversions on return value

Question

Consider the following C++ code:

struct B { };
struct A
{
        A(int);
        A(A&); // missing const is intentional
        A(B);
        operator B         


        

Answer 1

I don't think that "too many steps to figure on its own" as DeadMG pointed out is the reason. I've had constructs with 3-4 conversions, and the compiler always figured them out just fine.

I believe the problem is rather that the compiler is not allowed to convert a const reference to a non-constreference on its own behalf (it is only allowed to do that when you explicitly tell it with a cast).
And since the reference to the temporary object that is passed to the copy constructor is const, but the copy constructor is not, it doesn't find a suitable function.

EDIT: I didn't find any "real" code (see comments below) but constructed a multi-zigzag-convert example that actually compiles without errors under gcc 4.5. Note that this compiles just fine with -Wall -Wextra too, which frankly surprises me.

struct B
{
    signed int v;
    B(unsigned short in) : v(in){}
};

struct C
{
    char v;
    C(int in) : v(in){}
};

struct A
{
    int v;
    A(B const& in) : v(in.v){}
    operator C() { return C(*this); }
};

enum X{ x = 1 };

int main()
{
    C c = A(x);
    return 0;
}