Lecture of 24 January 1996

Homework

29 January

Note that no more than a short paragraph of explanation is necessary to answer these two questions adequately.

• Exercise 6 page 56. (Provide the requested code in either language.)
• Exercise 7 page 56.

5 February

• Exercise 1 page 73.
• Exercise 5 page 74.

Classes and Methods (cont.)

• Object Pascal Notes
  • Classes declared in units.
  • All public types, instance variables, and functions (methods) are declared within the interface part of the unit.
  • All private constants and variables, and the definitions of all methods of the class are provided within the implementation part of the unit.
  • Scope resolution mechanism is for specifying the class to which a method belongs (class.method).
• Smalltalk Notes
  • Browser (groups classes into categories for viewing, creation, editing, etc.)
  • Literal symbols (#name has value #name)
  • Class declaration includes
    • name of class
    • name of superclass
    • instance variable names
    • class variable names
    • class category (for browser)
  • Method names and parameter names for methods taking arguments are written using a keyword style (keyword:)
  • Assignment arrow ( <- )
  • Return value specifically signalled with up-arrow ( ^ )
  • Methods and instance variables can have the same name.
  • Variables are untyped.
  • All instance variables are inaccessible except in class methods.
  • All methods are accessible in any method.
• Objective C Notes
  • Programs may (and should) be divided by files into interface files (file.h) and implementation files (file.m)
  • Instance variables are declared in the header files but inaccessible outside the class methods.
  • import is used as a unique include mechanism.
  • Class interface specifies
    • name of class
    • instance variables
    • method prototypes
  • The type id is used to indicate a value which is a pointer to any arbitrary object. This follows the untyped variable idea of Smalltalk.
  • C types and object classes are distinct and do not mix!
  • void is used to specify methods (and functions) returning no value.
  • Each method parameter must have a specified type (id is the default type).
  • Class implementations specify the bodies of the methods noted in the class interface.
  • Objects variables (variables of type id) always contain a pointer to a heap-storage object.
• C++ Notes
  • Supports the interface/implementation file model.
  • Class declarations provide same information as interface in Objective-C.
  • Variables and parameters can be declared to be const. (The word const should follow the specification of the type to which it refers!).
  • Class definitions introduce new types and variables bound directly to objects (not pointers to objects) can be declared.
  • Member functions are simply function fields in a record thus, one cannot give the same name to a member function and a data member.
  • Declaration of inline functions is supported.

    More computing sins are committed in the name of efficiency (without necessarily achieving it) than for any other signle reason--including blind stupidity. --William Wulf

  • Scope resolution mechanism is for specifying the class to which a method belongs (class::method).