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

This is because C++ Standard allows only one user-defined conversion. According to §12.3/4:

At most one user-defined conversion (constructor or conversion function) is implicitly applied to a single value.

B oB = a; // not tried: ob( a.operator T*() ), 1 conversion func+1 constructor
oB = a;   // OK: oB.operator=( a.operator T*() ), 1 conversion func+1 operator=

As a workaround you can use explicit form of calling the constructor:

B oB( a ); // this requires only one implicit user-defined conversion