Chair of Software Engineering ATOT - Lecture 14, 19 May 2003 1 Advanced Topics in Object Technology Bertrand Meyer

ATOT - Lecture 14, 19 May 2003

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Chair of Software Engineering

Advanced Topics in Object Technology

Bertrand Meyer


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Lecture 14:

Advanced inheritance mechanisms


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Deferred classes

deferred class STACK [G]

feature

put (x: G) is-- Push x on top of stack.

requirenot full

deferredensure

item = xnot empty

end


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The STACK class (cont’d)

remove is-- Pop top element of stack.

requirenot empty

deferredensure

not fullcount = old count – 1

end


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full: BOOLEAN is-- Is there no room place for new items?

deferredend

empty: BOOLEAN is-- Is there no item?

deferredend

count: BOOLEAN is-- Number of items on stack

deferredensure

Result >= 0end


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-- Not all features need be deferred!

replace (x: G) is-- Replace top element of stack by x.

requirenot empty

doremoveput (x)

ensurenot emptyitem = xcount = old count

end

invariant

not (full and empty)

end


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Applications of deferred classes

Taxonomy Library organization Capturing common abstractions Capturing common behaviors “Don’t call us, we’ll call you” Analysis High-level architecture and design


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EiffelBase: Container structures

CONTAINER*

BOX* COLLECTION* TRAVERSABLE*

FINITE* INFINITE*

BOUNDED* UNBOUNDED* COUNTABLE*

RESIZABLE*

BAG* SET* HIERARCHICAL* LINEAR*

TABLE* ACTIVE* INTEGER_ INTERVAL

* BILINEAR*

INDEXABLE* CURSOR_ STRUCTURE

* DISPENSER* SEQUENCE*

ARRAY STRING HASH_TABLE STACK* QUEUE*

… …


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deferred class VAT

inherit

TANK

feature

in_valve, out_valve: VALVE

fill is-- Fill the vat.

requirein_valve.openout_valve.closed

deferredensure

in_valve.closedout_valve.closedis_full

end

empty, is_full, is_empty, gauge, maximum, ... [Other features] ...

invariant

is_full = (gauge >= 0.97 * maximum) and (gauge <= 1.03 * maximum)

end

Object-oriented analysis


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Indirect and direct repeated inheritance

A

B C

D

A

D


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Repeated inheritance

Assume class TAXPAYER with attributes

age: INTEGERaddress: STRINGbank_account: ACCOUNTtax_id: INTEGER

and routines such as

pass_birthday is do

age := age + 1 end

pay_taxes is ...

deposit_to_account (sum: INTEGER) is ...

TAXPAYER addresstax_idpass_birthday

age

pay_taxes


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Repeated inheritance (cont’d)

Heirs may include SWISS_TAXPAYER and US_TAXPAYER.

TAXPAYER addresstax_id

age

pay_taxespass_birthday

US_ TAXPAYER

SWISS_ TAXPAYER


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Repeated inheritance (cont’d)

The two above classes may in turn have a common heir: SWISS_US_TAXPAYER.

TAXPAYER addresstax_id


US_ TAXPAYER

SWISS_ TAXPAYER

SWISS_US_ TAXPAYER


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Repeated inheritance issues

What happens with features inherited twice from the common ancestor TAXPAYER, such as address, age, tax_id, pass_birthday?


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The inheritance clause

inherit

SWISS_TAXPAYERrename

address as swiss_address, tax_id as swiss_tax_id,pay_taxes as pay_swiss_taxes,bank_account as swiss_bank_account,deposit_to_account as deposit_to_swiss_account,...

end

US_TAXPAYERrename

address as us_address, tax_id as us_tax_id,pay_taxes as pay_us_taxes, bank_account as us_bank_account,deposit_to_account as deposit_to_us_account,...

end


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Sharing and replication

Features such as age and birthday, not renamed along any of the inheritance paths, will be shared.

Features such as tax_id, inherited under different names, will be replicated.

TAXPAYERaddresstax_id


US_ TAXPAYER

SWISS_ TAXPAYER

SWISS_US_ TAXPAYER

address us_addresstax_id us_tax_idpay_taxes pay_us_taxes

address swiss_addresstax_id swiss_tax_idpay_taxes pay_swiss_taxes


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The need for select

Assume there is a redefinition somewhere along the way:

TAXPAYER address

US_ TAXPAYER

SWISS_ TAXPAYER

SWISS_US_ TAXPAYER

address++address++

address us_address address swiss_address


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The need for select (cont’d)

A potential ambiguity arises because of polymorphism and dynamic binding:

t: TAXPAYERs: SWISS_TAXPAYERu: US_TAXPAYERsu: SWISS_US_TAXPAYER

if ... thent := s

elset := su

end...print (t.address)


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Removing the ambiguity

class SWISS_US_TAXPAYER

inherit

SWISS_TAXPAYERrename

address as swiss_address, tax_id as swiss_tax_id,pay_taxes as pay_swiss_taxes,bank_account as swiss_bank_account,deposit_to_account as deposit_to_swiss_account,...

selectswiss_address, swiss_tax_id, pay_swiss_taxes, swiss_bank_account, deposit_to_swiss_account

end

US_TAXPAYERrename

address as us_address, tax_id as us_tax_id,...

end


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Creating with a specified type

To avoid this:

a1: Ab1: B...create b1.make (...)a1 := b1

Simply use

a1: A...create {B} a1.make (...)

A

B C


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Once routines

If instead of

r isdo

... Instructions ...end

you write

r isonce

... Instructions ...end

then Instructions will be executed only for the first call by any client during execution. Subsequent calls return immediately.

In the case of a function, subsequent calls return the result computed by the first call.


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Scheme for shared objects

class SHARED_OBJECTS

feature

error_window: WINDOW isonce

create Result.make (...) end

exit_button: BUTTON isonce

create Result.make (...) end

...end

class MY_APPLICATION_CLASS

inherit

SHARED_OBJECTS

feature

r is do

error_window.put (my_error_message)end

...end


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Undefining a feature

deferred class B

inherit

Aundefine

fend

feature

...

end


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Feature merging

A B C

D

f* f* f+


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Feature merging (cont’d)

class D

inherit

A

B

C

feature

...

end


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Feature merging: with different names

A B C

D

g* f* h+

g f h f


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Feature merging: with different names

class D

inherit

Arename

g as f end

B

Crename

h as f end

feature...

end


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Feature merging: effective features

a1: A b1: B c1: C d1: Da1.g b1.f c1.h d1.f

A B C

D

g* f* h+

g f h ff- f-


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Feature merging: effective features

class D

inherit

Arename

g as f undefine

fend

B

Crename

h as f undefine

fend

feature...

end


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When is a name clash acceptable?

(Between n features of a class, all with the same name, immediate or inherited.)

They must all have compatible signatures.

If more than one is effective, they must all come from a common ancestor feature under repeated inheritance.


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Feature adaptation clauses

rename export undefine redefine select


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Export adaptation

class B

inherit

Aexport

{ANY} all{NONE} h{A, B, C, D} i, j, k

end

feature

...


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End of lecture 14

Documents

Chair of Software Engineering ATOT - Lecture 14, 19 May 2003 1 Advanced Topics in Object Technology Bertrand Meyer