Eiffel

							          "Man cannot discover new oceans
          unless he has the courage to lose
          sight of the shore."

          -- Andre Gide




Eiffel

         Eiffel
     Naeem Esfahani
     University of Tehran
I prefer to have as little as
possible to do with Bertrand
Meyer
       -- Bjarne Stroustrup, 1989
      Overview
•   Introduction & History
•   Design By Contract™
•   Elements
•   Concepts
•   Syntax and Semantics
Introduction & History
    Bertrand Meyer
• BS from Ecole polythecnique

• MS from Stanford University

• PhD from Univesite du Nancy

• Professor of Software Engineering at
  ETH in Zurich 2001
     Bertrand Meyer
• Nine years in a large company

• Three years on the faculty at the
  University of California, Santa Barbara

• computer languages, object-oriented
  system design, architectural reviews,
  technology assessment
     History
• Designed at Eiffel Software in 1985 as an
  internal tool

• A modern, OO environment integrating the
  concepts of modern software engineering

• There was simply nothing available
     History
• First demonstrated in public at the first OOPSLA
  conference in October of 1986

• Release it as a commercial product at the end of
  1986

• In 1988 in a book by Bertrand Meyer

• Version 2.3, released in the Summer of
  1990
     History
• Eiffel 3, was written entirely in Eiffel
  – Melting Ice Technology for fast recompilation
  – Fully graphical environment
  – Considerable advances in libraries
  – Optimization of the generated code


• The latest milestones is:
  Eiffel 5 and EiffelStudio
     Application
• Leading to a set of successful industrial
  projects in the US, Canada, Europe and
  the Far East

• Adoption by numerous universities as the
  primary teaching language
    Where the Name does come
    from?
• Homage to Gustave Eiffel, the man who
  built the eponymous Tower in Paris

• The Eiffel Tower was completed on time
  and within budget

• Small number of robust, elegant design
  patterns, combined and varied
  repeatedly to yield a powerful,
  efficient structure
     Where the Name does come
     from?
• The Eiffel Tower was initially conceived as
  a temporary structure and it was able to
  endure far beyond its original goals

• What better symbol could there be of the
  engineering principles behind Eiffel?
Design By Contract™
     Assertions
• A boolean expression that is evaluated
  when it is reached during execution

• If true, execution continues
• else, execution may halt or an exception

• Eiffel has support for writing assertion
     Assertions
Preconditions:
  When a routine is called

Postconditions:
  When a routine returns

General assertions:
  When execution reaches them

Class invariants:
  Maintained by all instances of a class
      Pre and postconditions
• Preconditions and postconditions are associated with
  routines of a class
    Pre and postconditions
• The preconditions must be true when the
  routine is called

• Postconditions must have been
  established when the routine terminates
      Class Invariant
• Conditions that must be true for all objects of the
  class at ‘stable’ times

• When method starts to execute:
   – Its preconditions are met and the class invariant is
     satisfied

• After execution:
   – The postcondition must be met and the class
     invariant must be satisfied
Class Invariant
Elements
     Classes
• The basic and only construct in Eiffel

• The attributes of entities and the
  operations that entities can perform

• A class represents all objects of that
  type
     Libraries
• Classes that frequently appear
  – Reuse


• EiffelBase:
  – INTEGER, REAL, STRING, LISTs, ARRAYs


• Libraries are not defined as part of
  the Eiffel language
     Features
• Each class has a set of features which
  represent the attributes and routines of a
  class

• routines are either procedures or
  functions; attributes can be fields,
  constants or functions
     Features
• Procedures (Commands) alter the state of
  the object

• Functions (Queries) are return an answer
  to a query about the state of an object

• This is by convention, rather than
  being enforced in Eiffel
Concepts
      Inheritance
• Build new classes out of existing classes, and to
  reuse features already defined in those classes,
  you use inheritance

• Eiffel has multiple inheritance
   – solves clashing by having a rename clause
   – Redefinition

• Inheritance is one of the fundamental
  mechanisms for reuse

• Polymorphism
Class Syntax
     Genericity
• You can reuse like inheritance

• Genericity is important in making programs type
  safe without resorting to type casts

• constrained genericity
  – allows generic parameters to be constrained


• allow you to write general algorithmic
  patterns
      Objects
• A name in an Eiffel program is declared as
  having a type. The declaration
    x:T

• Still does not refer to any objects: x is not bound
  to an object

• Expressed as the object void. We can see if an
  object is bound to void by writing x=void

• Name x can be bound to any object that
  type conforms to type T
     Objects
• Three ways to achieve this binding:

Assignment instruction: The assignment x:=y
  binds x to the object to which y is currently
  bound

A creation instruction: The creation instruction
  !!x creates a new object of type T,and binds
  x to it. This is similar to new in C++.

Routine call
     Objects
c: C
!! c.make
• An object of type C is created and attached to
   the reference c

!D! c.make
• An object of type D, where D conforms to C is
  created and attached to c.

• If you have a creation routine declared for
  the class, the creation routine must be
  called like constructor
      Objects
• Creation routines can be called as normal routines

• Note that the !! syntax is somewhat cryptic, and a recent
  change to the language has changed this for a create
  command keyword

• Eiffel has no delete operator. This is because, as with
  Java, Eiffel is garbage collected
       Etc
• Class variables: variables which do not have one copy
  per class of objects. The Eiffel equivalent for doing this is
  once routines

• Eiffel does not have...
   – Gotos are not needed, as the Eiffel style is to write small
     routines
   – Global variables are a sign of poor structuring use once
     routines instead
   – Type casts to make up for a flawed type system
   – Pointers with their associated problems


• Code must be structured in classes
Syntax and Semantics
     Some constructs
• Comments are introduced by --

• Grouped entities are terminated by the
  keyword end, no begin keyword

• No semicolons, optionally be placed
  between instructions
     Style
• Keywords are shown in bold
• User named entities in italic
• Class names are given in uppercase
• Eiffel is not case sensitive, so it is up to
  the programmer to follow style
  conventions.
• More than one words separate the
  constituent words with underscore ‘_’
     Access specifiers
• Any set of features introduced by the
  feature keyword can be exported to other
  specific classes

• ANY and NONE

• There is no strict equivalent to private, as
  Eiffel believes it is not sensible to restrict
  visibility in subclasses.
Access specifiers
    Basic Types
• BOOLEAN
  not, or, and, implies, or else, and then


• INTEGER
  +, -, *, //, \\, ˆ, <, >, <=, >=


• REAL
  +, -, *, /, ˆ, <, >, <=, >=
Conditional
     Iterations
• There is only one form of iteration in Eiffel
Procedures
    Functions
• The value to be returned
    result := expression
Redefinition
Renaming
         Counter
class
         COUNTER

feature -- Access
item: INTEGER -- Counter's value.

feature -- Element change
increment is -- Increase counter by one.
      do
             item := item + 1
      end
decrement is -- Decrease counter by one.
      do
             item := item - 1
      end
reset is -- Reset counter to zero.
      do
             item := 0
      end
end
Questions
       If Time!
•   Native C and C++
•   Simplicity
•   First release instead prototype
•   Melting ice