Class

[jimin-kiim]

• Data Abstraction and class
• Components of class
• Message
• Avoiding data members in the public interface

[jimin-kiim]

Data Abstraction and Class

Data Abstraction is a concept and the class is fundamental unit of data abstraction in C++

• Data Abstraction
  • creating classes with appropriate functionality, which hide the unnecessary details
  • a programming and design technique that relies on the separation of interface and implementation.
• Data Abstraction is realized by class in C++. Using the class means utilizing the data abstraction

[jimin-kiim]

Components of class

• Behavior(method, member functions, actions)
  • the actions that an instance can perform in response to a request.
  • parts of the method
    • name : matched to a message to determine
    • signature : the combination of return type and argument type. methods with the same name can be distinguished by different signatures
    • body : the code that will be executed when the method is invoked in response to a message
• State(variable, attributes, data members, data fields)
  • the data that an object must maintain in order to successfully complete its behavior.

[jimin-kiim]

Message

• a message is always given to some object, called the receiver.
• the action performed in response is determined by the receiver, different receivers can do different actions in response to the same message
• message passing syntax : ${message receiver}.${message selector} (${arguments});

[jimin-kiim]

Avoiding data members in the public interface

• making all the member variables to be private variable is desirable
• why
  • for consistency
  • for precise control over the accessibility of data members
    • precise controls : read-only, read-write, write-only
  • functional abstraction
    • can replace the data member with a computation not directly using it
• accessor(getter) : a method that simply returns an internal data value
  • to make the data read-only
  • provides better documentation that the data field is accessible
  • make it easier to later change the access behavior
• mutator(setter) : a method used to change the variable of an object

Visibility Modifier

• differentiate the interface and implementation views of a class
• public
  • external view (interface, sevice)
  • can be seen and manipulated by anybody (all clients)
• private
  • internal view(implementation)
  • accessible only by the class implementators
  • can be accessed only within the member functions of the class
• protected

[jimin-kiim]

Writing memory safe classes

• Avoid making copies of objects. Copying an object is expensive
• Avoid creating new objects. Try to reuse existing objects
• Use const reference parameters when appropriate
• Use const member functions
• Use pointers instead of references as data members.
• Avoid storage allocation in the default constructor. Delay it until the member is accessed.
• Use reference counting wherever possible.

Resist tricks in the initial stage

• Stick with safety first; make sure no memory leaks exist
• Don’t worry about optimization in the early stages of development.

[jimin-kiim]

Client’s responsibilities with classes and functions

• Understand the purpose of the class.
• Clearly understand what the class implementor expects from you, the client.
• Pay attention to every member function; in particular, const member functions are safer
• Understand the arguments being passed.
• Understand what your responsibility is when pointers and references are returned from functions.
• If the class documentation and the information in the header file differ, get clarification as to which is correct one before using the class
• Prefer functions that accept arguments that are pointers and references to const. They are safer.
• Don’t rely on any undocumented class details that the class implementor might have told you. Stick to the class interface and documentation.
• Be wary of classes that don’t implement the minimum set of member functions