Finish Constructors

• He discusses copy constructors.
  • What is this and when is it called?
  • What are the parameters?
  • The compiler will create one for you if you don't have one.
    • This will call the constructor of all member objects.
    • Then it will do a shallow copy
      • Unless a object has a deep copy constructor
  • you can delete or default a copy constructor if you wish.
  • You can call a copy constructor explicitly
  • He reminds us that we should copy or otherwise initialize ALL fields in the copy constructor.
  • He discusses pass by reference and pass by const reference.
• If your class has a container you wish to initialize, you can use an inititializer_list
  • a reference.
  • and another
  • Assume you have a class that has a container.
    • You want to be able to do MyClass a = {1,2,3,4};
    • You do not want to declare a vector, initialize it copy the data and pass it.
  • The solution is to use an initializer_list constructor.
    • You need to include initializer_list
    • You declare a parameter initializer_list<type< data
  • Note there are very few operations implemented on an intializer_list
    • begin, end, size and a constructor.
  • The documentation says
    • The lists are automatically constructed
    • The lifetime is temporary
    • These constructors take precedence over other constructors.
  • By the way, this is not limited to constructors.
  • Apparently the STL is fully compatible with initializer lists.
  • Look at initList.cpp
• A delegating constructor is a constructor that calls another constructor.
  • His example allows construction with a string by calling a convert string to double.
  • My example casts a float to int.

  •         PersonT(int a): name("none"), age(a) {
               cout << "in the age constructor for PersonT" << endl;
            }
    
            PersonT(double a): PersonT(static_cast<int>(a)) {
                cout << "in the delegated constructor for PersonT" << endl;
                cout << "\tparameter: " << a << " age: " << age << endl;
            } 

• Look at demo2.cpp
• He provides a nice table on 223 discussing when the compiler will generate constructors for you.