Eiffel Programming Language

1
Eiffel Programming Language
2

• Chad Frommeyer
• CSC 407/507
• Fall 2005
• Dr. Richard Fox

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History

• 1985 Language Development Began
• Developed by Bertrand Meyer of Interactive
  Software Engineering
• 1986 First Compiler Delivered
• 1987 Commercial Applications Developed
• 1991 NICE Founded (Non-Profit International
  Consortium for Eiffel)
• NICE controls evolution, standardization and
  basic class definitions for Eiffel
• 1996 Commercial Eiffel based development system
  becomes available (iss-base).
• Decendent of Algol and ADA

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Overview

• Pure object oriented language
• Strong statically typed
• Automatic memory management/Garbage collection
• Supports ADTs
• Supports Generic Classes
• Supports By Value and By reference semantics
• Promotes simplicity (Readable, not Writeable)
• Non-Object Oriented Capabilities/Low Level
  Functionality (C-Lang)
• Some Compilers only generate C source code
• Design By Contract (Reliability)
• Exception Handling
• Supports separate library compilation
• Supports In-Class Documentation
• Root class starts execution

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Overview (Continued)

• Statement delimiter () allowed, not required,
  typically used in muti-statement line
• Is not case sensitive
• Doesnt support global variables
• Doesnt support union types
• Doesnt support goto instructions
• Doesnt contain side-effect expression operators
• Doesnt support pointers or pointer arithmetic

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Hello World
indexing description Basic Hello World
author Jim Developer class
HELLO_WORLD creation make feature make is
do io.put_string ("Hello,
world!N") end end
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Basic Instructions

• Assignment
• Object Creation
• Routine Call
• Conditional
• Iteration
• Choice/Switch/Case

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Assignment

• i i 1
• Assignments cannot happen directly to class
  attributes. Methods/Routines must be used.
• Shortcut Assignments dont exist

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Object Creation

• Declaration accACCOUNT
• acc is void when declared
• At runtime acc obtains an object by calling
• create acc
• Which creates a new instance of ACCOUNT and
  attaches acc
• acc can now be used
• acc.open(John)
• acc.deposit(5000)

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Data Types

• The following data types exist, the
  initialization of variables of these types is
  automatically initialized
• INTEGER initializes to zero
• REAL and DOUBLE initialize to 0.0
• BOOLEAN initializes to false
• CHARACTER initializes to null
• Reference types initialize to a null reference
• INTEGER, REAL, DOUBLE, BOOLEAN and CHARACTER are
  all considered Expanded types

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Reference Types

• A reference is the default object type, when an
  instance of a class is created it is called a
  reference, this is created by either calling
  create or using !!

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Expanded Types

• An expanded type is one that is already
  initialized
• INTEGER, REAL, DOUBLE, BOOLEAN and CHARACTER are
  all considered Expanded types
• Expanded types dont require calling create or
  !!
• If the class is not defined with the keyword
  expanded then it will be a reference type.

expanded class INTEGER feature ... end
-- INTEGER
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Routine/Function Call
acc.open ("Jill") acc.deposit (5000) if
acc.may_withdraw(3000) then
acc.withdraw(3000)print(acc.balance) end
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Conditional
if x gt 10 then ... statements ... elseif
x gt 5 then ... elsif statements ...
elseif x gt 0 then ... more elsif
statements ... else ... else statements
... end
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Looping/Iteration

• Only one looping statement exists, but it could
  be used to emulate other types of loops.

For Loop
While Loop
Repeat Loop
from i 1 until i 10 loop
io.put_int (i) io.new_line i i
1 end
from node first until node
Void loop io.put_string (node.text)
node node.next end
from done False until done and
pages 10 loop done True
printer.output_next pages pages 1
end
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Choice/Switch/Case

• The inspected value must be enumerable

State INTEGER State_1, State_2, State_3
INTEGER is unique ... statements ... inspect
State when State_1 then ... statements
... when State_2 then ... statements ... when
State_3 then ... statements ... else ...
statements ... end
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Generic Classes
class STACK T feature push( element T
) is do storage( pos )
element pos pos 1 end
-- push end -- STACK
class LUNCH_COUNTER feature tray_stack
STACK TRAY napkin_dispenser STACK
NAPKIN ... init is do
... napkin_dispenser.pop(
end -- init end -- LUNCH_COUNTER
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Creation Routines/Constructors

• A creation routine is called when the reference
  type is created with create or !!

class CONVERTER creation make feature
temperature DOUBLE make is do
temperature 98.6 end -- make
... end -- CONVERTER
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Exception Handling

• Exceptions can be thrown in few cases
• Design by contract failures
• Low level functions
• Rescue (Catch)
• Retry (can only exist within a rescue clause)
• Retry starts execution of the routine again
  without the variable initialization

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Exception Handling (Cont.)
read_next_character (f FILE) is -- Make
next character available in last_character
-- if impossible, set failed to True.
require readable file . readable
local impossible BOOLEAN do
if impossible then failed
True else last_character
low_level_read_function ( f ) end
rescue impossible True
retry end
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Design By Contract

• Facilitates more reliable techniques
• Defines correct usage
• Assertions (Boolean Expression)
• Precondition (require)
• Postcondition (ensure)
• Class invariants (invariant)
• Class invariant must be satisfied upon exit of
  the creation procedure (constructor)

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Assertion Monitoring

• Assertion monitoring levels are set at compile
  time
• The levels vary from no monitoring to monitoring
  all require/ensure/invariant
• Exceptions will be thrown if assertions are being
  monitored
• If the exception isnt handled, a run-time error
  will result

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Sample DBC
indexing description "Simple bank accounts"
class ACCOUNT feature -- Access
balance INTEGER -- Current balance
deposit_count INTEGER is --
Number of deposits made since opening
do As before end
feature -- Element change deposit (sum
INTEGER) is -- Add sum to account.
require non_negative sum gt
0 do As before
ensure one_more_deposit
deposit_count old deposit_count 1
updated balance old balance sum
end
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Sample DBC (Cont.)
feature NONE -- Implementation
all_deposits DEPOSIT_LIST invariant
consistent_balance (all_deposits / Void)
implies (balance
all_deposits . total) zero_if_no_deposits
(all_deposits Void) implies
(balance 0) end -- class ACCOUNT
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Object Oriented

• Purely Object Oriented
• Everything is an object
• Information Hiding
• Encapsulation
• Polymorphism/Dynamic Binding
• Inheritance (Including Multiple)

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Object Oriented (Cont.)

• Supports information hiding/encapsulation
• No attributes of a class are allowed to be
  modified directly. All modifications must happen
  within a subroutine
• No global variables are allowed
• No static functions are allowed
• Secret attributes/routines are equivalent to
  private variables/methods

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Polymorphism

• Dynamic binding allows polymorphic object to call
  the appropriate versioned routine

acc ACCOUNT sav SAVINGS_ACCOUNT acc sav
acc.deposit( 1000 )
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Inheritance

• Inheritance is supported
• Multiple inheritance is supported
• Routine can be overridden (redefine)
• Parent is known as a precursor
• Keyword precursor can be used to reference the
  parent
• Renaming allows conflicts with multiple
  inheritance to be resolved

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Inheritance (Cont.)
indexing description "Savings accounts"
class SAVINGS_ACCOUNT inherit ACCOUNT
redefine deposit end feature --
Element change deposit ( sum INTEGER ) is
-- Add sum to account. do
precursor (sum)
end Other features end -- class
SAVINGS_ACCOUNT
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Inheritance (Cont.)

• The implementation of inheritance supplies many
  keywords to define how the parents members are
  recognized
• Rename allows renaming of a parent
  attribute/routine
• Export allows changing protection of a parent
  attribute/routine
• Redefine allows overriding a routine
• Undefine allows removing a routine

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Inheritance (Cont.)
class D inherit A rename
g as f -- g was effective in A
export X, Y, feature1, feature2
undefine f end B
undefine f end -- f was effective in
B C -- C also has an effective feature f ,
which will serve as -- implementation for the
result of the join. feature
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In-Class Documentation

• Keyword Indexing
• Indexing Items (author, description, other)
• Developer defined indexing items
• Developer tools exist to generate documentation

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class ACCOUNT feature balance INTEGER --
Attribute owner PERSON minimum_balance
INTEGER is 1000 open (who PERSON) is --
Routine -- Assign the account to
owner who. do owner
who end deposit (sum INTEGER) is
-- Deposit sum into the account.
do add (sum) end
withdraw (sum INTEGER) is --
Withdraw sum from the account. do
add (-sum) end may_withdraw
(sum INTEGER) BOOLEAN is -- Function
-- Is there enough money to withdraw sum?
do Result (balance gt sum
minimum_balance) - Return value end
feature NONE add (sum INTEGER) is -
Private/Secret Routine -- Add sum to
the balance. do balance
balance sum end end -- class ACCOUNT
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Bibliography

• http//en.wikipedia.org/wiki/Eiffel_programming_la
  nguage
• http//archive.eiffel.com/doc/online/eiffel50/intr
  o/language/
• http//www.eiffel.com/index.html
• http//www.comp.ufla.br/monserrat/eiffel/advanced
  _introduction/eiffel.html