PHP面向对象深入研究之【组合模式与装饰模式】

组合模式

定义：组合模式定义了一个单根继承体系，使具有截然不同职责的集合可以并肩工作。

一个军队的案例，

<?php

abstract class Unit { // 个体
    abstract function bombardStrength();
}

class Archer extends Unit { // 弓箭手
    function bombardStrength() {
        return 4;
    }
}

class LaserCannonUnit extends Unit { // 火炮手
    function bombardStrength() {
        return 44;
    }
}
?>

军队整合成员，输出火力

<?php

abstract class Unit {
    abstract function bombardStrength();
}

class Archer extends Unit {
    function bombardStrength() {
        return 4;
    }
}

class LaserCannonUnit extends Unit {
    function bombardStrength() {
        return 44;
    }
}


class Army { // 军队
    private $units = array(); // 定义私有属性 个体集

    function addUnit( Unit $unit ) { // 添加成员
        array_push( $this->units, $unit );
    }

    function bombardStrength() { // 火力
        $ret = 0;
        foreach( $this->units as $unit ) {
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }
}

$unit1 = new Archer(); 
$unit2 = new LaserCannonUnit(); 
$army = new Army();
$army->addUnit( $unit1 ); 
$army->addUnit( $unit2 ); 
print $army->bombardStrength(); // 输出火力
?>
output:
48

军队进一步整合其他军队

<?php

abstract class Unit {
    abstract function bombardStrength();
}

class Archer extends Unit {
    function bombardStrength() {
        return 4;
    }
}

class LaserCannonUnit extends Unit {
    function bombardStrength() {
        return 44;
    }
}


class Army {
    private $units = array();
    private $armies= array();

    function addUnit( Unit $unit ) {
        array_push( $this->units, $unit );
    }

    function addArmy( Army $army ) {
        array_push( $this->armies, $army );
    }

    function bombardStrength() {
        $ret = 0;
        foreach( $this->units as $unit ) {
            $ret += $unit->bombardStrength();
        }

        foreach( $this->armies as $army ) {
            $ret += $army->bombardStrength();
        }

        return $ret;
    }
}

$unit1 = new Archer(); 
$unit2 = new LaserCannonUnit(); 
$army = new Army();
$army->addUnit( $unit1 ); 
$army->addUnit( $unit2 ); 
print $army->bombardStrength();
print "\n";
$army2 = clone $army; // 克隆军队
$army->addArmy( $army2 );
print $army->bombardStrength();
print "\n";
?>
output:
48
96

更好的方式，支持新增，移除等等其他功能。

<?php
abstract class Unit {
    abstract function addUnit( Unit $unit );
    abstract function removeUnit( Unit $unit );
    abstract function bombardStrength();
}
class Army extends Unit { // 军队
    private $units = array();

    function addUnit( Unit $unit ) {
        if ( in_array( $unit, $this->units, true ) ) { // $this用于调用正常的属性或方法，self调用静态的方法，属性或者常量
            return;
        }
        
        $this->units[] = $unit;
    }

    function removeUnit( Unit $unit ) {
        // >= php 5.3
        $this->units = array_udiff( $this->units, array( $unit ), 
                       function( $a, $b ) { return ($a === $b)?0:1; } );

        // < php 5.3
        // $this->units = array_udiff( $this->units, array( $unit ), 
        //                create_function( '$a,$b', 'return ($a === $b)?0:1;' ) ); 
        // 对象数组，create_function,创建函数
    }

    function bombardStrength() {
        $ret = 0;
        foreach( $this->units as $unit ) {
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }
}

// quick example classes
class Tank extends Unit {  // 坦克
    function addUnit( Unit $unit ) {}
    function removeUnit( Unit $unit ) {}

    function bombardStrength() {
        return 4;
    }
}

class Soldier extends Unit {  // 士兵
    function addUnit( Unit $unit ) {}
    function removeUnit( Unit $unit ) {}

    function bombardStrength() {
        return 8;
    }
}

$tank =  new Tank();
$tank2 = new Tank();
$soldier = new Soldier();

$army = new Army();
$army->addUnit( $soldier );
$army->addUnit( $tank );
$army->addUnit( $tank2 );

print_r( $army );
print $army->bombardStrength()."\n";

$army->removeUnit( $soldier );

print_r( $army );
print $army->bombardStrength()."\n";
?>
output:
Army Object
(
    [units:Army:private] => Array
        (
            [0] => Soldier Object
                (
                )

            [1] => Tank Object
                (
                )

            [2] => Tank Object
                (
                )

        )

)
16
Army Object
(
    [units:Army:private] => Array
        (
            [1] => Tank Object
                (
                )

            [2] => Tank Object
                (
                )

        )

)
8

添加异常处理

<?php
abstract class Unit {
    abstract function addUnit( Unit $unit );
    abstract function removeUnit( Unit $unit );
    abstract function bombardStrength();
}

class Army extends Unit {
    private $units = array();

    function addUnit( Unit $unit ) {
        if ( in_array( $unit, $this->units, true ) ) {
            return;
        }
        
        $this->units[] = $unit;
    }

    function removeUnit( Unit $unit ) {
        // >= php 5.3
        //$this->units = array_udiff( $this->units, array( $unit ), 
        //                function( $a, $b ) { return ($a === $b)?0:1; } );

        // < php 5.3
        $this->units = array_udiff( $this->units, array( $unit ), 
                        create_function( '$a,$b', 'return ($a === $b)?0:1;' ) );
    }

    function bombardStrength() {
        $ret = 0;
        foreach( $this->units as $unit ) {
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }
}

class UnitException extends Exception {}

class Archer extends Unit {
    function addUnit( Unit $unit ) {
        throw new UnitException( get_class($this)." is a leaf" );
    }

    function removeUnit( Unit $unit ) {
        throw new UnitException( get_class($this)." is a leaf" );
    }

    function bombardStrength() {
        return 4;
    }
}

$archer = new Archer();
$archer2 = new Archer();
$archer->addUnit( $archer2 );

?>

output:
Fatal error: Uncaught exception 'UnitException' with message 'Archer is a leaf'

点评：组合模式中的一切类都共享同一个父类型，可以轻松地在设计中添加新的组合对象或局部对象，而无需大范围地修改代码。

最终的效果，逐步优化(完美)：

<?php

class UnitException extends Exception {}

abstract class Unit {
    abstract function bombardStrength();

    function addUnit( Unit $unit ) {
        throw new UnitException( get_class($this)." is a leaf" );
    }

    function removeUnit( Unit $unit ) {
        throw new UnitException( get_class($this)." is a leaf" );
    }
}

class Archer extends Unit {
    function bombardStrength() {
        return 4;
    }
}

class LaserCannonUnit extends Unit {
    function bombardStrength() {
        return 44;
    }
}

class Army extends Unit {
    private $units = array();

    function addUnit( Unit $unit ) {
        if ( in_array( $unit, $this->units, true ) ) {
            return;
        }
        
        $this->units[] = $unit;
    }

    function removeUnit( Unit $unit ) {
        // >= php 5.3
        //$this->units = array_udiff( $this->units, array( $unit ), 
        //                function( $a, $b ) { return ($a === $b)?0:1; } );

        // < php 5.3
        $this->units = array_udiff( $this->units, array( $unit ), 
                        create_function( '$a,$b', 'return ($a === $b)?0:1;' ) );
    }

    function bombardStrength() {
        $ret = 0;
        foreach( $this->units as $unit ) {
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }
}

// create an army
$main_army = new Army();

// add some units
$main_army->addUnit( new Archer() );
$main_army->addUnit( new LaserCannonUnit() );

// create a new army
$sub_army = new Army();

// add some units
$sub_army->addUnit( new Archer() );
$sub_army->addUnit( new Archer() );
$sub_army->addUnit( new Archer() );

// add the second army to the first
$main_army->addUnit( $sub_army );

// all the calculations handled behind the scenes
print "attacking with strength: {$main_army->bombardStrength()}\n";
?>
output:
attacking with strength: 60

更牛逼的组合处理，

<?php

abstract class Unit {
    function getComposite() {
        return null;
    }

    abstract function bombardStrength();
}


abstract class CompositeUnit extends Unit { // 抽象类继承抽象类
    private $units = array();

    function getComposite() {
        return $this;
    }

    protected function units() {
        return $this->units;
    }

    function removeUnit( Unit $unit ) {
        // >= php 5.3
        //$this->units = array_udiff( $this->units, array( $unit ), 
        //                function( $a, $b ) { return ($a === $b)?0:1; } );

        // < php 5.3
        $this->units = array_udiff( $this->units, array( $unit ), 
                        create_function( '$a,$b', 'return ($a === $b)?0:1;' ) );
    }

    function addUnit( Unit $unit ) {
        if ( in_array( $unit, $this->units, true ) ) {
            return;
        }
        $this->units[] = $unit;
    }
}
class Army extends CompositeUnit {

    function bombardStrength() {
        $ret = 0;
        foreach( $this->units as $unit ) {
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }

}

class Archer extends Unit {
    function bombardStrength() {
        return 4;
    }
}

class LaserCannonUnit extends Unit {
    function bombardStrength() {
        return 44;
    }
}

class UnitScript {
    static function joinExisting( Unit $newUnit,
                                  Unit $occupyingUnit ) { // 静态方法，直接通过类名来使用
        $comp;

        if ( ! is_null( $comp = $occupyingUnit->getComposite() ) ) { // 军队合并处理
            $comp->addUnit( $newUnit ); 
        } else { // 士兵合并处理
            $comp = new Army(); 
            $comp->addUnit( $occupyingUnit );
            $comp->addUnit( $newUnit );
        }
        return $comp;
    }
}

$army1 = new Army();
$army1->addUnit( new Archer() );
$army1->addUnit( new Archer() );

$army2 = new Army();
$army2->addUnit( new Archer() );
$army2->addUnit( new Archer() );
$army2->addUnit( new LaserCannonUnit() );

$composite = UnitScript::joinExisting( $army2, $army1 );
print_r( $composite );

?>

output:
Army Object
(
    [units:CompositeUnit:private] => Array
        (
            [0] => Archer Object
                (
                )

            [1] => Archer Object
                (
                )

            [2] => Army Object
                (
                    [units:CompositeUnit:private] => Array
                        (
                            [0] => Archer Object
                                (
                                )

                            [1] => Archer Object
                                (
                                )

                            [2] => LaserCannonUnit Object
                                (
                                )

                        )

                )

        )

)

点评：Unit 基础，CompositeUnit复合中实现add与remove。军队继承Composite，射手继承Archer。这样射手中就不会有多余的add与remove方法了。

装饰模式

装饰模式帮助我们改变具体组件的功能。

看例子

<?php
abstract class Tile { // 砖瓦
    abstract function getWealthFactor(); // 获取财富
}

class Plains extends Tile { // 平原
    private $wealthfactor = 2;
    function getWealthFactor() {
        return $this->wealthfactor;
    }
}

class DiamondPlains extends Plains { // 钻石地段
    function getWealthFactor() {
        return parent::getWealthFactor() + 2;
    }
}

class PollutedPlains extends Plains { // 污染地段
    function getWealthFactor() {
        return parent::getWealthFactor() - 4;
    }
}
$tile = new PollutedPlains();
print $tile->getWealthFactor();
?>
output:
-2

点评：不具有灵活性，我们不能同时获得钻石与被污染的土地的资金情况。

装饰模式使用组合和委托而不是只使用继承来解决功能变化的问题。
看例子：

<?php

abstract class Tile {
    abstract function getWealthFactor();
}

class Plains extends Tile {
    private $wealthfactor = 2;
    function getWealthFactor() {
        return $this->wealthfactor;
    }
}

abstract class TileDecorator extends Tile { // 装饰
    protected $tile;
    function __construct( Tile $tile ) {
        $this->tile = $tile;
    }
}

class DiamondDecorator extends TileDecorator { // 钻石装饰
    function getWealthFactor() {
        return $this->tile->getWealthFactor()+2;
    }
}

class PollutionDecorator extends TileDecorator { // 污染装饰
    function getWealthFactor() {
        return $this->tile->getWealthFactor()-4;
    }
}

$tile = new Plains();
print $tile->getWealthFactor(); // 2

$tile = new DiamondDecorator( new Plains() );
print $tile->getWealthFactor(); // 4

$tile = new PollutionDecorator(
             new DiamondDecorator( new Plains() ));
print $tile->getWealthFactor(); // 0
?>
output:
2
4
0

点评：这个模型具有扩展性。我们不需要创建DiamondPollutionPlains对象就可以构建一个钻石被污染的对象。

一个更逼真的例子

<?php

class RequestHelper{} // 请求助手

abstract class ProcessRequest { // 进程请求
    abstract function process( RequestHelper $req );
}

class MainProcess extends ProcessRequest { // 主进程
    function process( RequestHelper $req ) {
        print __CLASS__.": doing something useful with request\n";
    }
}

abstract class DecorateProcess extends ProcessRequest { // 装饰进程
    protected $processrequest;
    function __construct( ProcessRequest $pr ) { // 引用对象，委托
        $this->processrequest = $pr;
    }
}

class LogRequest extends DecorateProcess { // 日志请求
    function process( RequestHelper $req ) {
        print __CLASS__.": logging request\n"; // 当前类,有点递归的感觉
        $this->processrequest->process( $req );
    }
}

class AuthenticateRequest extends DecorateProcess { // 认证请求
    function process( RequestHelper $req ) {
        print __CLASS__.": authenticating request\n";
        $this->processrequest->process( $req );
    }
}

class StructureRequest extends DecorateProcess { // 组织结构请求
    function process( RequestHelper $req ) {
        print __CLASS__.": structuring request\n";
        $this->processrequest->process( $req );
    }
}

$process = new AuthenticateRequest( new StructureRequest(
                                    new LogRequest (
                                    new MainProcess()
                                    ))); // 这样可以很灵活的组合进程的关系，省去很多重复的继承

$process->process( new RequestHelper() );
print_r($process);
?>

output:
AuthenticateRequest: authenticating request
StructureRequest: structuring request
LogRequest: logging request
MainProcess: doing something useful with request
AuthenticateRequest Object
(
    [processrequest:protected] => StructureRequest Object
        (
            [processrequest:protected] => LogRequest Object
                (
                    [processrequest:protected] => MainProcess Object
                        (
                        )

                )

        )

)

点评：这里有一种递归的感觉，一层调用一层。模式是牛人总结出来用于灵活的解决一些现实问题的。牛！给开发多一点思路。