Why constructor is not called for given casting operator?

Question

struct A {}; 
struct B
{
  B (A* pA) {}
  B& operator = (A* pA) { return *this; }
};

template
struct Wrap
{
  T *x; 
  operator T* () { return         


        

Answer 1

It's because you're using "copy initialization". If you write the declaration of oB:

B oB(a);

, it should work. The semantics of the two initializations are different. For B oB(a), the compiler tries to find a constructor which can be called with the given arguments. In this case, B::B(A*) can be called, because there is an implicite conversion from Wrap to A*. For B oB = a, the semantics are to implicitly convert a to type B, then use the copy constructor of B to initialize oB. (The actual copy can be optimized out, but the legality of the program is determined as if it weren't.) And there is no implicit conversion of Wrap to B, only of Wrap to A*.

The assignment works, of course, because the assignment operator also takes a A*, and so the implicit conversion comes into play.