inheritance

[Tony Johansson]

Hello!!

I'm reading a book about C++ and there is something that I don't understand
so I ask you.

The book says
"The set of all public features of a class is called a public inteface, or
simply interface. When the inheritance hierarchy is
properly designed, the derived class interface conforms to the base class
interface. This leads to the substitutability principle:
Whenever the base class object is expected, you can use an object of a
derived class. For example, if an object of class BankAccount is expected,
you can instead use an object of the class CheckingAccount or of the class
SavingAccount.
You may violate the substitutability principle if you override a
nonpolymorphic operation"

Question 1.
What does they mean with this last line. "You may violate the
substitutability principle if you override a nonpolymorphic operation."

Question 2.What does they mean with "When the inheritance hierarchy is
properly designed, the derived class interface conforms to the base class
interface."

//Tony

 

[Teddy]

so many topices
so many questions

just tell us the name of the book you are reading

 

[Tony Johansson]

It's called Programming with design pattern.
//Tony

 

[Alf P. Steinbach]

* Tony Johansson:

Hello!!

I'm reading a book about C++ and there is something that I don't understand
so I ask you.

The book says
"The set of all public features of a class is called a public inteface, or
simply interface. When the inheritance hierarchy is
properly designed, the derived class interface conforms to the base class
interface. This leads to the substitutability principle:
Whenever the base class object is expected, you can use an object of a
derived class. For example, if an object of class BankAccount is expected,
you can instead use an object of the class CheckingAccount or of the class
SavingAccount.
You may violate the substitutability principle if you override a
nonpolymorphic operation"

Question 1.
What does they mean with this last line. "You may violate the
substitutability principle if you override a nonpolymorphic operation."

Assuming a "nonpolymorphic operation" is a non-virtual function: you cannot
override a non-virtual function.

Question 2.What does they mean with "When the inheritance hierarchy is
properly designed, the derived class interface conforms to the base class
interface."

Read up on the Liskov Substitution Principle.

 

[Pete Becker]

Question 1.
What does they mean with this last line. "You may violate the
substitutability principle if you override a nonpolymorphic operation."

It again means that the writing is sloppy. My guess is that it's
supposed to be saying that if the correct behavior of the derived class
requires replacing (not overriding) a non-virtual base class function
then the derived class cannot be used where the base type is expected.
Which, if you think about it, ought to be fairly clear: calling the base
version of that function won't do what the derived type needs.

Question 2.What does they mean with "When the inheritance hierarchy is
properly designed, the derived class interface conforms to the base class
interface."

Fuzzy thinking. "conforms to" doesn't mean anything here.

I'll renew my earlier suggestion: get a different book.