Class member without a default constructor

Question

Suppose I have a class A without a default constructor, a factory method factoryA that returns an object of type A, and a class B that has A as its member. I know that in th

Answer 1

Member objects are always initialized before entry into the body (the part between the curly braces) of the constructor. If you don't mention a member in the initializer list, it gets default constructed. So mention it!

B::B(int j) : _a(factoryA(0 < j)) { };

This calls the function factoryA with the argument value true if j is greater than 0 and false otherwise, and initializes the member _a with the value returned by that call.