享元模式

目的

为了最大限度地减少内存使用,Flyweight 会尽可能地与类似的对象共享内存。当使用了大量相似状态的对象时,Flyweight 就会派上用场。通常的做法是,将状态保存在外部数据结构中,在需要的时候将其传递给 flyweight 对象。

UML 类图

享元模式类图

代码

Text.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Flyweight;

/**
* This is the interface that all flyweights need to implement
*/
interface Text
{
public function render(string $extrinsicState): string;
}

Word.php

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<?php

namespace DesignPatterns\Structural\Flyweight;

class Word implements Text
{
private string $name;

public function __construct(string $name)
{
$this->name = $name;
}

public function render(string $font): string
{
return sprintf('Word %s with font %s', $this->name, $font);
}
}

Character.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Flyweight;

/**
* Implements the flyweight interface and adds storage for intrinsic state, if any.
* Instances of concrete flyweights are shared by means of a factory.
*/
class Character implements Text
{
/**
* Any state stored by the concrete flyweight must be independent of its context.
* For flyweights representing characters, this is usually the corresponding character code.
*/
private string $name;

public function __construct(string $name)
{
$this->name = $name;
}

public function render(string $font): string
{
// Clients supply the context-dependent information that the flyweight needs to draw itself
// For flyweights representing characters, extrinsic state usually contains e.g. the font.

return sprintf('Character %s with font %s', $this->name, $font);
}
}

TextFactory.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Flyweight;

use Countable;

/**
* A factory manages shared flyweights. Clients should not instantiate them directly,
* but let the factory take care of returning existing objects or creating new ones.
*/
class TextFactory implements Countable
{
/**
* @var Text[]
*/
private array $charPool = [];

public function get(string $name): Text
{
if (!isset($this->charPool[$name])) {
$this->charPool[$name] = $this->create($name);
}

return $this->charPool[$name];
}

private function create(string $name): Text
{
if (strlen($name) == 1) {
return new Character($name);
} else {
return new Word($name);
}
}

public function count(): int
{
return count($this->charPool);
}
}

测试

Tests/FlyweightTest.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Structural\Flyweight\Tests;

use DesignPatterns\Structural\Flyweight\TextFactory;
use PHPUnit\Framework\TestCase;

class FlyweightTest extends TestCase
{
private array $characters = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',
'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];

private array $fonts = ['Arial', 'Times New Roman', 'Verdana', 'Helvetica'];

public function testFlyweight()
{
$factory = new TextFactory();

for ($i = 0; $i <= 10; $i++) {
foreach ($this->characters as $char) {
foreach ($this->fonts as $font) {
$flyweight = $factory->get($char);
$rendered = $flyweight->render($font);

$this->assertSame(sprintf('Character %s with font %s', $char, $font), $rendered);
}
}
}

foreach ($this->fonts as $word) {
$flyweight = $factory->get($word);
$rendered = $flyweight->render('foobar');

$this->assertSame(sprintf('Word %s with font foobar', $word), $rendered);
}

// Flyweight pattern ensures that instances are shared
// instead of having hundreds of thousands of individual objects
// there must be one instance for every char that has been reused for displaying in different fonts
$this->assertCount(count($this->characters) + count($this->fonts), $factory);
}
}