c++ Constructor initializer list with complex assignments

How about adding some static transformation methods?

class C {
  private:
    static B transform1(D&);
    static B transform2(D&);
  public:
    A a;
    C(D d) :
      a{transform1(d),transform2(d)}
      {}
};

Related:

• Is there any problem of calling functions in the initialization list?
• Is it ok to call a function in constructor initializer list?
• can member functions be used to initialize member variables in an initialization list?

I would use pointers in this case, Here's the modified version of your example:

//Class A is not modified
/* a class without a default constructor */
class A {
  public:
    B x1
    B x2
    A(B x1_, B x2_) : x1{x1_}, x2{x2_} {};
};



/* a class that contains an A object and needs to initialize it based on some complex logic */
class C {
  public:
    A* a;   // I declare this as a pointer
    C(D d)
      {
          // Perform all the work and create b1,b2
          a = new A(b1, b2);
      }

    ~C()    // Create a destructor for clean-up
    {
          delete a;
    }

};

Using the new operator I can initialize the object whenever I want. And since the object is in the class scope, I delete it in the destructor (at the end of the class scope)