120 lines
2.9 KiB
Markdown
120 lines
2.9 KiB
Markdown
---
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title: php的闭包特性
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date: 2017-01-11 18:39:17
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category: notes
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tags:
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- php
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keywords:
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- php
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- 闭包
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- lambada
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- 匿名函数
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---
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闭包和匿名函数在`PHP 5.3.0`引入，并且PHP将两者视为相同的概念。闭包其实是伪装成函数的对象，它的实质其实是`Closure`实例。
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创建闭包非常简单：
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```php
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$c = function($name) {
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return sprintf("Hello World! Hello %s!", $name);
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};
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echo $c('PHP');
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```
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使用`use`对闭包附加状态，多个参数使用`,`分隔：
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```php
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function callPerson($name) {
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return function($about) use ($name) {
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return sprintf("%s, %s", $name, $about);
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}
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}
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$triver = callPerson('Triver');
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echo $triver("slow down, please!!");
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```
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附加的变量会被封装到闭包内，即使返回的闭包队形已经跳出了`callPerson()`的作用域也仍然会记住`$name`的值。
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闭包有一个有趣的`bindTo()`方法，可以将闭包的内部状态绑定到其他对象上，第二个参数指定了绑定闭包的对象所属的类，从而实现在闭包中访问绑定对象的私有方法和属性。
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```php
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class Bind {
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protected $name = 'no name';
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public $change;
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public function addAction($action) {
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$this->change = $action->bindTo($this, __CLASS__);
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}
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}
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$bind = new Bind();
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$bind->addAction(function() {
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$this->name = "php";
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return $this->name;
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});
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$change = $bind->change;
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echo $change();
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```
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使用这个特性可以方便的为类添加方法并绑定：
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```php
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trait MetaTrait
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{
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//定义$methods数组,用于保存方法（函数）的名字和地址。
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private $methods = array();
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//定义addMethod方法，使用闭包类绑定匿名函数。
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public function addMethod($methodName, $methodCallable)
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{
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if (!is_callable($methodCallable)) {
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throw new InvalidArgumentException('Second param must be callable');
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}
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$this->methods[$methodName] = Closure::bind($methodCallable, $this, get_class());
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}
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//方法重载。为了避免当调用的方法不存在时产生错误，
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//可以使用 __call() 方法来避免。
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public function __call($methodName, array $args)
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{
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if (isset($this->methods[$methodName])) {
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return call_user_func_array($this->methods[$methodName], $args);
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}
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throw RunTimeException('There is no method with the given name to call');
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}
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}
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class HackThursday {
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use MetaTrait;
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private $dayOfWeek = 'Thursday';
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}
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$test = new HackThursday();
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$test->addMethod('when', function () {
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return $this->dayOfWeek;
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});
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echo $test->when();
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```
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php7 中增加了 `Closure::call()` 方法，可以更高效的绑定对象作用域并调用。
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```php
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class A {private $x = 1;}
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// Pre PHP 7 code
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$getXCB = function() {return $this->x;};
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$getX = $getXCB->bindTo(new A, 'A'); // intermediate closure
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echo $getX();
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// PHP 7+ code
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$getX = function() {return $this->x;};
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echo $getX->call(new A);
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```
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