C++ program part5

1. What is your reaction to this line of code?

   delete this;

   
   It's not a good practice.
   A good programmer will insist that the statement is never to be used if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.
   The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the pointer can and usually does lead to disaster.
   A reader pointed out that a class can ensure that its objects are instantiated on the heap by making its destructor private. This idiom necessitates a kludgy DeleteMe kind of function because the instantiator cannot call the delete operator for objects of the class. The DeleteMe function would then use "delete this."
   I got a lot of mail about this issue. Many programmers believe that delete this is a valid construct. In my experience, classes that use delete this when objects are instantiated by users usually spawn bugs related to the idiom, most often when a program dereferences a pointer to an object that has already deleted itself.
   
   
2. What is a default constructor?
   A constructor that has no arguments or one where all the arguments have default argument values.
   If you don't code a default constructor, the compiler provides one if there are no other constructors.
   If you are going to instantiate an array of objects of the class, the class must have a default constructor.
   
   
3. What is a conversion constructor?
   A constructor that accepts one argument of a different type.
   The compiler uses this idiom as one way to infer conversion rules for a class. A constructor with more than one argument and with default argument values can be interpreted by the compiler as a conversion constructor when the compiler is looking for an object of the type and sees an object of the type of the constructor's first argument.
   
   
4. What is the difference between a copy constructor and an overloaded assignment operator?
   A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
   First, you must know that a copy constructor is one that has only one argument, which is a reference to the same type as the constructor. The compiler invokes a copy constructor wherever it needs to make a copy of the object, for example to pass an argument by value. If you do not provide a copy constructor, the compiler creates a member-by-member copy constructor for you.
   You can write overloaded assignment operators that take arguments of other classes, but that behavior is usually implemented with implicit conversion constructors. If you do not provide an overloaded assignment operator for the class, the compiler creates a default member-by-member assignment operator.
   This discussion is a good place to get into why classes need copy constructors and overloaded assignment operators. By discussing the requirements with respect to data member pointers that point to dynamically allocated resources, you demonstrate a good grasp of the problem.