匿名函數
匿名函數（Anonymous function），也叫閉包函數（closures），允許臨時創(chuàng)建一個沒有指定名稱的函數，最經常用作回調函數（callback）參數的值。
匿名函數的實現
匿名函數是目前是通過Closure類來實現，匿名函數會產生這個類的對象。自PHP 5.4起，這個類帶有一些方法，允許在匿名函數創(chuàng)建后對其進行更多的控制。
注意：PHP手冊特別說明__invoke()這個魔術方法與匿名函數的實現過程無關。
Closure類如下：
Closure {
/* 方法 */
__construct ( void )
public static Closure bind ( Closure $closure , object $newthis [, mixed $newscope = 'static' ] )
public Closure bindTo ( object $newthis [, mixed $newscope = 'static' ] )
}Closure::__construct — 用于禁止實例化的構造函數Closure::bind — 復制一個閉包，綁定指定的$this對象和類作用域。Closure::bindTo — 復制當前閉包對象，綁定指定的$this對象和類作用域。匿名函數例子：
$func = function($str){
echo $str;};$func('hello');閉包
閉包是指在創(chuàng)建時封裝周圍狀態(tài)(如變量)的函數，即使閉包所在的環(huán)境的不存在了，閉包中封裝的狀態(tài)依然存在。
閉包的實現
將匿名函數放在一個普通函數中（也可以將匿名函數返回），就構成了一個閉包。
function closureFunc(){
$func = function(){
echo 'hello';
}
$func();}closureFunc();//輸出:hello閉包的使用
在匿名函數中引入局部變量時需要用到use關鍵字。這是因為PHP中的變量范圍只在它的生效范圍中。在匿名函數里并沒有對變量進行定義，所以需要使用use關鍵字
function closureFunc1(){
$num = 1;
$func = function() use($num){
echo $num;
};
$func();}closureFunc2();//輸出閉包返回匿名函數并傳參
function closureFunc2(){
$num = 1;
$func = function($str) use($num){
echo $num;
echo $str;
};
return $func;}$func = $closureFunc2();$func('hello');//輸出 1 hello以上，歡迎討論~
把閉包簡單理解成“定義在一個函數內部的函數”。
所以，在本質上，閉包就是將函數內部和函數外部連接起來的一座橋梁。
四、閉包的用途
閉包可以用在許多地方。它的最大用處有兩個，一個是前面提到的可以讀取函數內部的變量，另一個就是讓這些變量的值始終保持在內存中。
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