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<?OOps! The PHP Fear and
Loathing Guide to Basic Object-Oriented Design
terry chaytagged
11 February 2009engineering brownbag
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{introduction2XtremePeople
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“PhpPatterns is just that—a source of design patterns for PHP code. Will wonders never cease? I ran this by a Java programmer I know that I have drawn into the PHP world and her comment was, ‘I’d have never even thought to try patterns in PHP.’”
—the FuzzyBlog
phppatterns? {
object-orientedsnob
{
{
Web Developer Training
PHP to ASP.NET
{
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“ASP.NET applications are based on a robust Object Oriented Programming (OOP) paradigm rather than a scripting paradigm…The upside of ASP.NET’s support of OOP concepts [vs PHP] means that ASP.NET applications for the most part run better designed code, have clear separation of content, logic, and data and thus are generally easier to support over the long term.”
—Migrating from PHP to ASP.NET
dotFUD {
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“Although being a young fellow myself, I have to hold my hand up and say I was educated in an era before design patterns were even invented. Yes it’s true, such a time did exist. In my day, it was called ‘Data Structures’.”
—Alan Williamson, Editor-in-ChiefNovember 2002
datastructures? {
grumpyoldprogrammer
{
the middle way
{
離
11守
破
threelevels{
離
12守
破
shuhold
chinese character “house” and “law”
to abide by; to defend
the o-o bigot
7 habits: dependence
{
離
13守
破
habreakchinese character “stone” + phonetic
to break
the grumpy old programmer
7 habits: independence
{
離
14守
破
rileave
chinese character “bird” + phonetic
to leave; to depart
the middle way
7 habits: interdependence
{
Some basic O-O
{
16
myquiz 1:<?php 2:$tests[1] = new stdClass(); 3:$tests[2] = new stdClass(); 4: 5:foreach ($tests as $obj) { 6: $obj->foo = 'bar'; 7:} 8: 9:print_r($tests); 10:?>
1.
2.
3.tychay$ php test.php Array ( [1] => stdClass Object ( )
[2] => stdClass Object ( )
)
{1. construct some generic PHP objects2.interate over objects and assign them a value3.dump the array of objects
what do you think the output of this is and why?
UNEXPECTED!
1:<?php 2:$tests[1] = new stdClass(); 3:$tests[2] = new stdClass(); 4: 5:foreach ($tests as $obj) { 6: $obj->foo = 'bar'; 7:} 8: 9:print_r($tests); 10:?>
17
myquiz
remember that PHP4, objects are like everything else, so you need the &!
Otherwise it will use a copy of the object.
{
1:<?php 2:$tests[1] =& new stdClass(); 3:$tests[2] =& new stdClass(); 4: 5:foreach ($tests as $count=>$obj) { 6: $tests[$count]->foo = 'bar'; 7:} 8: 9:print_r($tests); 10:?>
18
myquiz
tychay$ php answer1.php Array ( [1] => stdClass Object ( [foo] => bar )
[2] => stdClass Object ( [foo] => bar )
)
now we’ve fixed the problem!
{
19
byreference{
remember this is true also when:
prints empty object!
1:<?php 2:class testClass 3:{ 4: function addObject(&$object) 5: { 6: $this->object = $object; 7: } 8:} 9:$testObject =& new testClass(); 10: 11:function addBar($object) 12:{ 13: $object->bar = 'this is set also'; 14:} 15:addBar($testObject); 16: 17:function getSameObject() 18:{ 19: global $testObject; 20: return $testObject; 21:} 22:$returnObject = getSameObject(); 23:$returnObject->same = 'this should be in object'; 24: 25:class testRefClass 26:{ 27: function testRefClass($objFromHell) 28: { 29: $objFromHell->something = 'something here'; 30: $objFromHell->addObject($this); 31: } 32:} 33:$tempObject = new testRefClass($testObject); 34:print_r($testObject); 36:?>
1. passing parameters
3. constructor
2. functions that return objects
20
{ 1:<?php 2:class testClass 3:{ 4: function addObject(&$object) 5: { 6: $this->object = $object; 7: } 8:} 9:$testObject =& new testClass(); 10: 11:function addBar(&$object) 12:{ 13: $object->bar = 'this is set also'; 14:} 15:addBar($testObject); 16: 17:function &getSameObject() 18:{ 19: global $testObject; 20: return $testObject; 21:} 22:$returnObject =& getSameObject(); 23:$returnObject->same = 'this should be in object'; 24: 25:class testRefClass 26:{ 27: function testRefClass(&$objFromHell) 28: { 29: $objFromHell->something = 'something here'; 30: $objFromHell->addObject($this); 31: } 32:} 33:$tempObject =& new testRefClass($testObject); 34:print_r($testObject); 36:?>
byreferenceremember this is true also when:
1. passing parameters
3. constructor
2. functions that return objects
PHP5 fixes this!
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“…the new object model makes object oriented programming in PHP much more powerful and intuitive. No longer will you have to mess with cryptic & characters to get the job done. No longer will you have to worry about whether changes you made to the object inside the constructor will survive the dreaded new-operator behavior…
php5 {
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…No longer will you ever have to stay up until 2:00AM tracking elusive bugs!”
—Zeev SuraskiNovember 2002
php5 {
Zeev’s2AMbug
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staticproperties
no static class variables in PHP.
substitute with
global variables
static function variables (bad idea)
{
24
globalstaticbind by reference in constructor (or elsewhere)
1:<?php 2:$GLOBALS['_statics']['testClass']['staticCount'] = 0; 3:class testClass 4:{ 5: var $staticCount; 6: function testClass() 7: { 8: $this->staticCount =& $GLOBALS['_statics']['testClass']['staticCount']; 9: } 10: function increment() 11: { 12: return ++$this->staticCount; 13: } 14:} 15:$test1 =& new testClass(); 16:$test2 =& new testClass(); 17:$test1->increment(); 18:$test2->increment(); 19:print_r($test1); 20:print_r($test2); 21:echo testClass::increment(); 22:?>
tychay$ php test3.php testclass Object ( [staticCount] => 2 ) testclass Object ( [staticCount] => 2 ) 1
watch out though!
25
singletonone of the simplest patterns
creates a single instance of a class (DB connection)
lazy evaluation
flexible
1:<?php 2:class testSingleton 3:{ 4: function &instance() 5: { 6: static $singleton; 7: if (!$singleton) { 8: $singleton =& new testSingleton(); 9: } 10: return $singleton; 11: } 12:} 13:$test1 =& testSingleton::instance(); 14:$test1->foo = bar; 15:$test2 =& testSingleton::instance(); 16:print_r($test2); 17:?>
tychay$ php test4.php testsingleton Object ( )
watch out though!
26
singletonalso note the liberal use of &
1:<?php 2:$GLOBALS['_statics']['testSingleton']['singleton'] = null; 3:class testSingleton 4:{ 5: function &instance() 6: { 7: if (is_null($GLOBALS['_statics']['testSingleton']['singleton'])) { 8: $GLOBALS['_statics']['testSingleton']['singleton'] =& new testSingleton(); 9: } 10: return $GLOBALS['_statics']['testSingleton']['singleton']; 11: } 12:} 13:$test1 =& testSingleton::instance(); 14:$test1->foo = bar; 15:$test2 =& testSingleton::instance(); 16:print_r($test2); 17:?>
tychay$ php test5.php testsingleton Object ( [foo] => bar )
27
latebindingwhen a polymorphic call is resolved at run time (instead of compile time)
oo-bigots advocate against (speed, strong typing)
simple to do in PHP
1:<?php 2:class testLateBinding 3:{ 4: function callMeLate() 5: { 6: echo "I was called\n"; 7: $this->wasCalled = true; 8: } 9:} 10:$object1 =& new testLateBinding(); 11:$object2 =& new testLateBinding(); 12:$functionname = 'callMeLate'; 13: 14:$object1->{$functionname}(); 15: 16:call_user_func(array(&$object2,$functionname)); 17:print_r($object2); 18:?>
tychay$ php test6.php I was called I was called testlatebinding Object ( [wasCalled] => 1 )
variable-variablescall_user_func()
PHP4.3+note the &!.
{
28一
三二
roadmap
29一
三二
the why
why do old metaphors fail?
why use agile processes?
methodology
30一
三二
the what
what are the precepts of class rules
what are the parameters of package design
what are patterns?
principles
31一
三二
the how
how do patterns allow me to follow principles?
how can patterns work around a design error?
how do patterns apply to more than O-O?
patterns
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methodology一
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metaphors
一
一
34
codecomplete
Published 1993
Microsoft “Tome”
Award winning book
35
paradigm shift
Code Complete is a “wanna be” Structure of Scientific Revolutions
he uses “paradigm shift”
Key premise: key metaphor of software should be construction
一
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36 straw men
The metaphor o f construction is so central to the book, that the subtitle is: “A Practical Handbook of Software Construction.”
Thus i t needs to construct some straw men of failed metaphors in order to prove why we should adopt the “ so f tware a s construction” paradigm.
一
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一 1.software penmanship
“writing code”
causes expensive trial and error
focused on originality > reuse
“plan to throw one away”
“it might have been state-of-the-art software-engineering practice in 1975”
2.softwarefarming
一
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39
growing a system “piece by piece”
bad metaphor!
fertilizing a system plan?
thinning the detailed design?
increasing code yields through effective land managment?
harvesting code?
rotating in a crop of assembler?
Who ever believed this shit?
一
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why Code Complete sucks
software as construction
一
The #1 reason why software is not construction
一離
守
破
Mythical Man Month
This is a really famous essay from 1975. Does the year sound fami l i a r ? Yes , the Frederick Brooks is the same engineer treated with derision in Code Complete’s “Software as Writing” straw man.
A lot of what he says was controversial, but one thing that was never denied was the man -month wa s a myth . What is a mythical man month?
一
43 man-month
一the premise is that men and months a re interchangeable.
This means that in order to reach a deadline I simply add people to the project.
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44man-month
myth
The problem:
Adding people to a late project makes it later!
first consider case where they’re everything is partition-able (man-month).
then add constant time for training
then add communication: n(n-1)/2
compare with unpartitionable (single man)
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45
where?
man-hour (măn’our') n. An industrial unit of production equal to the work one person can produce in an hour. Source: The American Heritage® Dictionary of the English Language, Fourth Edition
fromconstruction!
一
programming!=labor
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Mythical Man-Month referred to five times in Code Complete
Including having the author give an endorsement on the back cover!
irony
php{con
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“I’d be astonished if the open-source community has in total done as many man-years of computer security code reviews as we have done in the last two months”
—Steven Lipner, Director of Security Assurance, Microsoft (April 8th, 2002)
persistantmyth
asengineeringsoftware…
一
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49
“The final goal of any engineering activity is some type of documentation. When a design effort is complete, the design documentation is turned over to the manufacturing team. If the design documents truly represent a complete design, the manufacturing team can proceed to build the product.”
—Jack Reeves, C++ Journal, 1992
一
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50
“Two Irreparable Mistakes of thre Software Field: 1. The believe that the source code is a development product, not the design for a product.”
—Michael Feathers, ObjectMentor
The other problem with software as construction:
the “design” phase finishes with working source code
it’s based on the illusion that the source code is the product!
一
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51
How did we buy this illusion?
“It is cheaper and simpler to build the design and test it than do anything else. We do not care how many builds we do—they cost next to nothing…No other modern industry would tolerate a rework rate of over 100% in its manufacturing process”
—Jack Reeves, C++ Journal, 1992
a software “build” means “manufacturing” phase is cheap.
一
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離
守
破
A software developer is more akin to an artist than an assembly line worker… Throwing more people into the design mix can be counterproductive.
—Jason Burkert
“Software as engineering” accepts the reality of the mythical man-month!
The source code is the design.
離
一
53
roadmap
一
三二
now that we’ve talked discussed the paradigm or metaphor it is time to apply that to programming practice.
54
heavyweight離
守
破
methodologies like ISO9001 violate “software as an engineering”
by definition
treat auxiliary documentation as the product
55
Note influence of construction metaphor
BDUF: Big Design Up Front
Big Bang Delivery
waterfall
SYSTEM
SPECIFICATION
REQUIREMENTS
ANALYSIS
ARCHITECTURAL
DESIGN
CODING AND
DEBUGGING
DETAILED DESIGN
UNIT TESTING
SYSTEM TESTING
MAINTAINENCE
from Code Complete, p.3
BDUF
Big Bang
一
56
changing requirements
constant release schedule
not life-death
“The reason why dynamic languages like Perl, Python, and PHP are so important … Unlike applications from the pre v ious parad igm, web applications are not released in one to three year cycles. They are updated every day, sometimes every hour.”
—Tim O’Reilly, 14 May 2003
websoftware
一
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“The biggest mistake in ‘Build one to throw away’ concept is that it implicitly assumes the classical sequential or waterfall model of software construction.”
—Frederick Brooks, Mythical Man-Month, 20th Aniv. 1995
moreirony一
agility
一
59
XP離
守
破
ship early and often!
one of many lightweight methodologies known as “agile”
I’ll cover three features of XP. So you get an idea of what is considered an “agile” process
一
1.Test-First Design
一
designbytest
recall the waterfall process. Look at where the unit testing is.
r eca l l the “ so f tware a s engineering” metaphor: tests and builds are cheap. Why aren’t we leveraging it?
We should be testing first and using testing as a design technique (the hard part of engineering), not a testing technique (easy part).
SYSTEM
SPECIFICATION
REQUIREMENTS
ANALYSIS
ARCHITECTURAL
DESIGN
CODING AND
DEBUGGING
DETAILED DESIGN
UNIT TESTING
SYSTEM TESTING
MAINTAINENCE
一
1:<?php 2:class MoneyBagTest extends TestCase { 3: var $m12CHF; 4: var $m14CHF; 5: var $m28USD; 6: var $mArray1; 7: var $moneybag1; 8: var $moneybag2; 9: function MoneyBagTest( $name = "MoneyBagTest" ) { 10: $this->TestCase( $name ); 11: } 12: 13: function setUp() { 14: $this->m12CHF = new Money( 12, "CHF" ); 15: $this->m14CHF = new Money( 14, "CHF" ); 16: } 17: function tearDown() { 18: $this->m12CHF = NULL; 19: $this->m14CHF = NULL; 20: $this->m28USD = NULL; 21: } 22: 23: function testSimpleAdd() { 24: $result = $this->m12CHF->add( $this->m14CHF ); 25: $this->assert(new Money(27,"CHF"), $result, "This should fail" ); 26: $this->assertEquals(new Money(27,"CHF"), $result, "This should fail" ); 27: } 28: 29: // insert more tests here: use "test..." for name of function. 30:} 31:
62
code unit test first
1. Code the Unit Test First
2. Write minimum code until test works
3. Refactor (see later)
4. Rerun tests
constructor
a test
一
fixture
keep the bar green to keep the code clean…
30:} 31: 32:$test = new MoneyBagTest(); 33:$testRunner = new TestRunner(); 34:$testRunner->run($test); 35:?> 一
2.Refactoring
一
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“The process of changing a software system in such a way that does not alter the external behavior of the code yet improves the internal structure”
—Martin Fowler, Refactoring, 1999
the changes by themselves are tiny
focus on simplicity (in design) not simplistic (implementation)
refactorit!一
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do this continuously
purpose of a module of code:
function it performs
allow change
communicate
prevents code rot in large projects
my experience.
refactorit!一
3.You Aren’t Going to Need It (YAGNI)
一
최태리68
Implement the simplest thing that could possibly work.
Basically, if you need it, you can put it in later—it does not “save time.”
Set aside your fears about tomorrow and concentrate on today.
whatisYAGNI?
최태리69
YAGNIperkskeeps system smaller and easier to understand (form of refactoring)
more likely to ship out the door if you focus on needs
allows for system accretion
recall how fast a web iteration vs. Big Bang
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70
“A project done in Java will cost 5 times as much, take twice as long, and be harder to maintain than a project done in a scripting language such as PHP or Perl,”
—Philip Greenspun 20 September 2003
최태리71
lack of rigid O-O definitely a plus!
recall the “Migrating from PHP to dotNET” document
lack of framework definitely a plus!
phpYAGNI
72
Well bad pattern for a loosly typed language such as PHP!
Iterator Pattern: provide a way to access the element of an aggregate object sequentially without exposing its underlying representation
badpatternAggregate
CreateIterator()
ConcreteAggregate+ CreateIterator()
Iterator+ First()+ Next()+ IsDone()+ CurrentItem()
ConcreteIterator
return new ConcreteIterator(&$this)
1:<?php 2://A lot of code in here... 3:include(ECLIPSE_ROOT.'ArrayIterator.php'); 4: 5:$iterator =& new ArrayIterator(&$arrayToBeIterated); 6:while ($element=$iterator->getCurrent()) { 7: echo $iterator->key().' => '.$element; 8: $iterator->next(); 9:} 10:$iterator->reset(); 11: 12:?>
iterator# phpdefault
You can vary what is being iterated over (ignoring constructor)
YAGNI!
If you must have an iterator there is SPL in PHP5!
1:<?php 2:foreach($arrayToBeIterated as $key=>$value) { 3: echo $key.' => '.$value; 4:} 5:?>
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pair programming
the planning game/user-stories
code reviews
acceptance tests
on-site customer
other processes: SCRUM, Crystal, etc.
code ownership
XPnotcovered一
75
roadmap
一
三二
the metaphor/paradigm for building software is engineering
we now know agility: the lightweight processes that avoid the waterfall process
離
守
破
76
roadmap
一
三二
What programming principles help us program correctly?
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principles二
78
roadmap
一
三二
1. What precepts for class design?
2. Grouping classes into packages using what parameters?
3. What are patterns?
precepts of classes
二
최태리80
single responsibility
A class should have only one reason to change.
Each responsibility is an axis of change.
more than one responsibility = coupling
二
81
violationPEAR is great.
Except…
This is the PEAR Error constructor. Note that this method causes the object to violate SRP!
2:function PEAR_Error($message = 'unknown error', $code = null, 3: $mode = null, $options = null, $userinfo = null) 4:{ 5: if ($mode === null) { 6: $mode = PEAR_ERROR_RETURN; 7: } 8: $this->message = $message; 9: $this->code = $code; 10: $this->mode = $mode; 11: $this->userinfo = $userinfo; 12: if (function_exists("debug_backtrace")) { 13: $this->backtrace = debug_backtrace(); 14: } 15: if ($mode & PEAR_ERROR_CALLBACK) { 16: $this->level = E_USER_NOTICE; 17: $this->callback = $options; 18: } else { 19: if ($options === null) { 20: $options = E_USER_NOTICE; 21: } 22: $this->level = $options; 23: $this->callback = null; 24: } 25: if ($this->mode & PEAR_ERROR_PRINT) { 26: if (is_null($options) || is_int($options)) { 27: $format = "%s"; 28: } else { 29: $format = $options; 30: } 31: printf($format, $this->getMessage()); 32: } 33: if ($this->mode & PEAR_ERROR_TRIGGER) { 34: trigger_error($this->getMessage(), $this->level); 35: } 36: if ($this->mode & PEAR_ERROR_DIE) {
82
and the violation goes on
callbacks
die
return mode
trigger_error
exception
35: } 36: if ($this->mode & PEAR_ERROR_DIE) { 37: $msg = $this->getMessage(); 38: if (is_null($options) || is_int($options)) { 39: $format = "%s"; 40: if (substr($msg, -1) != "\n") { 41: $msg .= "\n"; 42: } 43: } else { 44: $format = $options; 45: } 46: die(sprintf($format, $msg)); 47: } 48: if ($this->mode & PEAR_ERROR_CALLBACK) { 49: if (is_string($this->callback) && strlen($this->callback)) { 50: call_user_func($this->callback, $this); 51: } elseif (is_array($this->callback) && 52: sizeof($this->callback) == 2 && 53: is_object($this->callback[0]) && 54: is_string($this->callback[1]) && 55: strlen($this->callback[1])) { 56: @call_user_func($this->callback, $this); 57: } 58: } 59: if (PEAR_ZE2 && $this->mode & PEAR_ERROR_EXCEPTION) { 60: eval('throw $this;'); 61: } 62:} 63:?>
최태리83
Liskov substitution
Subtypes must be substitutable for their base types.
not an “is-a” relationship
validation of LSP occurs in the client! (Design By Contract).
二
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84
Design By Contract va l idates L i sko v Subst i tu ion . What va l idates Des ign by contract?
Unit Tests! Remember them? They determine define it.
In fact, PEAR PHPUnit can document a Design By Contract by reading the un i t te s t (aka TestDox).
1:<?php 2:require_once 'PHPUnit/Framework/TestCase.php'; 3: 4:class FooTest extends PHPUnit_Framework_TestCase 5:{ 6: public function testIsASingleton() {} 7: public function testAReallyLongNameIsAGoodThing() {} 8:} 9:?>
Foo - Is a singleton - A really long name is a good thing
I violate LSP
Look a t how na ïve th i s diagram is . It ’s the most obvious one but focuses on the physical objects instead of their behaviors.
The objects are defined in terms of the clients. Think about an image coming back from the camera, or trying to set a dimmer to a light switch that turns on or off only.
Unfortunately I had to live with it for reasons later.
Common
CameraSwitchable
Sensor
HVAC
최태리86
otherprecepts
Open-Closed Principle
Dependency-Inversion Principle
Interface Segregation Principle
二
parameters of packages
二
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88
“A few days ago, I was at Microsoft, and they held an amazing conference…After this conference, I was kinda depressed about the future of PHP and Apache…The ASP.NET stuff is just perfect. Fast, Secure and Robust. ASP.NET technology is better than PHP technology.”
—Sterling Hughes 5 June 2003
二
최태리
Common language Runtime
access to COM+
server ui controls
“code behind” (.cs)
server-side object model
event-driven handlers
automatic page state (ViewState)
built-in Validation object
try-catch
二
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built-in authentication (Web.config)
built-in database abstraction (ADO.NET) +
connection pooling + data binding
built-in MSXML: DOM, XSLT, SAX + Web Services
auto targeting of HTML
IDE (Visual Studio .NET)
built-in output caching
I see what Sterling is saying!However…
二
최태리
Common Language Runtime 2nd class, compiling cache, Pint (Parrot)
access to COM+ access to COM, Java, C/C++ extensions, mono, command line
server ui controls, “ViewState”- saving form state
PEAR::HTML_* (Form, Menu, Page…) + others + BYO
“code behind” smarty, fasttemplate, flexy, it, phplib, + others, BYO
server-side object model session, __sleep(), __wakeup(), SRM
event driven handlers bad idea, fusebox + zillions of others, s9y, BYO
output-caching zend accelerator, Cache, Cache_Lite, free energy, BYO
validation object PEAR::Validate + zillions of others
try-catch in PHP5. no substitute for proper error handling
“Web.config”- authentication auth, LiveUser, + others
ADO.Net- database abstraction db specific, dbx, PEAR DB, MDB, ADODB
connection pooling, data-binding pconnect, SRM, only nice on client-side
MSXML expat, DOM, SimpleXML, XMLtree etc., 2 SOAP, 5 XMLRPC
VisualStudio- IDE Komodo, Zend+ others, text editors
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92
離
守
破
All of them (or equivalent) can be done in PHP .
I have a choice on a solution—Zend’s solution doesn’t bankrupt someone else’s (or me!)
Most solutions are open source so I don’t have be tied to someone else’s release-upgrade cycle.
ASP.NET’s large framework violates YAGNI—encourages o-o bigotry and bad design.
二
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93
Compar ing PHP to ASP.NET i s l ike comparing the Linux kernel to the Windows Platform.
GNU/Linux is the kernel + too lcha in . That toolchain is based on a lot of small interacting programs that can be cha ined to c reate complex behavior.
Windows does the complicated approach.
we say Unix has…
二
cohesionvs coupling.
二
최태리95
Frameworks vs. Libraries
A good package is highly cohesive but weakly coupled. This creates high reusability.
Remember the J2EE taking 5x as long to build? This is why. Too much framework. When you use one part of a package, you reuse them all.
This is why PEAR succeeds…
二
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Some of these frameworks are great, but the best are reused entirely (i.e. shrink-wrapped).
and Frameworks failAriadne, Binary Cloud, Back-End, bBlog, COWeb, Eocene, ezPublish, FastFrame, FUDforum, ISMO, Komplete, LogiCreate Application Server, Mambo, MetaL, Midgard, more.groupware, NetUse, Nucleus, phpGroupWare, Phrame, PostNuke, PHPortal, phpWebSite, Rodin, SiteManager, serendipity, STPHPLib, tikiwiki, TUTOS, WordPress, XOOPS…
二
acyclic dependency
二
depend on stability
二
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99
this covers acyclic dependency
the more you depend on a package the more stable it must be (think client-centric)
recall my devices diagram…
Common
CameraSwitchable
Sensor
HVAC
二
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100
Caveat: I’m going to use that bad “construction” analogy…
The Leaning Tower of Pi sa wa s bu i l t on a shifting foundation. It’s been l ean ing s ince before it was finished.
Sounds like the what happens when you you try to extend someone else’s framework.
二
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101
This is a mapping of the PEAR XML package dependencies.
Not ice how weak l y coupled they are.
Notice the packages which are depended on. What happens if the API is changed.
What if you depend on them? Better have your Unit Tests!
XML_ParserXML_Util
XML_Beautifier
XML_CSSML
XML_Tree
XML_DTD
XML_fo2pdf
XML_HTMLSax
XML_image2svg
XML_NITF
XML_RSS
XML_SaxFilters
XML_Serializer
XML_sql2xml
XML_Statistics
XML_RDDL
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roadmap
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we now know the precepts by which classes are made
and the parameters by whic they are packaged into classes…
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roadmap
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Before we go discuss patterns it helps to define what a pattern is!
If we skip this then we run the danger of becoming a o-o bigot or a grumpy old programmer!
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what are patterns?
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Patterns come from a book on architecture:
“Each pattern describes a problem which occurs over and over again in our environment and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.”
—Christopher Alexander, The Timeless Way of Building, 1979
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I don’t know architecture.
It makes me think of the software construction metaphor
Let’s find some patterns closer to us…
Web Design!
whatever!
cookie crumbssolve deeply hierarchical navigation
tabssolve lateral
navigation along a few high level
elements
tabscan use a million
times over, without ever doing it the same way twice
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二definedbycontext
Let’s not be an o-o snob.
“tabs” and “cookie crumbs” are both navigational patterns. Which one is best to use is defined by context.
patterns are designed to be linked together
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?baddesigntale of the keyfob
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115mybane
Recall my poor design choice.
Now realize that a KeyFob has four buttons. Each one is a sensor.
Since I implemented the low level stuff blindly and this e r ror occurred on the presentation tier, the user sees one keyfob as four devices. One for each button!
Common
CameraSwitchable
Sensor
HVAC
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How to make four devices appear as one
?三
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!a pattern a day keeps the
pink slip away
composite pattern
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Common
Aggregate
A composite pattern adds a subclass that conta ins 1 o r more elements of the base class.
Thus i t appears to clients as a single object, even though it contains more than one and have to handle the objects behind the scenes.
Common
CameraSwitchable
Sensor
HVAC
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?phpdocdecoupled messaging
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121phpDocu
phpDocumentor is a PEAR l ibra r y /app l i ca t ion that tokenizes and parses your PHP code for JavaDoc style comments and uses them to build hyperlinked API docs.
The problem is the parsers (preg, tokenizer, c-based) and the renderers (various HTML, peardoc, XML, PDF) both will need to vary in the PHP5 version.
The event messaging that occurs can get quite complex.
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How to make a more robust messaging system
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!allow one object to notify
many (run-time config)
observer pattern
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An observer registers with the subject for notification using the attach() method passing itself.
The subject notifies all observers by calling its notify() which iterates over all observers and calls its update() method
You can pass $this to update ( ) to a l low observer to use subject.
Subject+ attach(&$observer)+ detatch(&$observer)# notify()
Observer+ update()
ConcreteObserver+ update()
ConcreteSubject
0..1*
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?templatesworking friendly with
designers
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shutemplatedotNet’s serverui controls and auto page state are great
but they’re template systems
however PHP IDE != Visual Studio
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1:<html> 2:<head> 3: <title>Example ASP.NET template</title> 4:</head> 5:<body> 6:<script language="VB" runat="server"> 7:Sub Page_Load(sender As Object, e As EventArgs) 8: TheDate.Text = DateTime.Now 9:End Sub 10:</script> 11: <p>The current date is: <asp:Label id="TheDate" runat="server" />.</p> 12:</body> 13:</html>
三shu
how does this render in an editor?
how does it separate model-view-controller?
does MVC really matter anyway?…
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“With Web applications, nearly all the engineering happens in the SQL database and the interaction design, which is embedded in the page flow links. None of the extra power of Java is useful…”
—Philip Greenspun 2003 September 20
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hatemplatePHP is itself a templating language.
if all web developers are PHP programmers this makes the most sense
however
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1:<html> 2:<head> 3: <title>Example ASP.NET template</title> 4:</head> 5:<body> 6:<script language="VB" runat="server"> 7:Sub Page_Load(sender As Object, e As EventArgs) 8: TheDate.Text = DateTime.Now 9:End Sub 10:</script> 11: <p>The current date is: <asp:Label id="TheDate" runat="server" />.</p> 12:</body> 13:</html>
1:<html> 2:<head> 3: <title>Example simple PHP version</title> 4:</head> 5:<body> 6: <p>The current date is: <?php echo date('l, F dS, y'); ?>.</p> 7:</body> 8:</html>
三shu ha
much smaller and easier to read!
how does a web designer deal with it?
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!doing templates without
o-o
freeenergy
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ritemplate1. check for compiled
version.
2. if compiled then include compiled version
3. if not compiled then call routine to compile template
4. use XML!
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1:<?php 2:tc::import('tips'); 3:tc::import('tc.error'); 4: 5:$template =& new tips(); 6:$template->assign('date',date('l, F dS, y')); 7:$template->output('tipsexample.html'); 8:?> Separate templates =
separate files
leverages shu
This is a smarttemplate like system
leverages ha of php
use XML so the web developer can work with
1:<tips:template> 2:<html> 3:<head> 4: <title>Example PHP template</title> 5:</head> 6:<body> 7: <p>The current date is: <tips:variable name="date">Wednesday, October 21st, 2003</tips:variable>.</p> 8:</body> 9:</html> 10:</tips:template>
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}conclusion
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?>questionsAndAnswers
三
http://homepage.mac.com/tychay/talks/oops
