In-depth understanding of php anonymous functions
PHP中, 传递Callback的方式, 一直很丑陋. 在PHP5.3以前, 我们只有俩种选择:
字符串的函数名 使用create_function的返回值
在PHP5.3以后, 我们多了一个选择, 也就是Closure,
$func = function () { ... };
array_walk($arr, $func);从实现上来说, 第一种方式: 传递函数名字符串是最简单的.
而第二种方式create_function, 其实和第一种方式本质上一样的, create_function返回一个字符串的函数名, 这个函数名的格式是:
"\000_lambda_" . count(anonymous_functions)++;
我们来看看create_function的实现步骤:
获取参数, 函数体
拼凑一个"function lambda_func (参数) { 函数体;} "的字符串
eval之
通过lambda_func在函数表中找到eval后得到的函数体, 找不到就出错
定义一个函数名:"\000_lambda_" . count(anonymous_functions)++
用新的函数名替换lambda_func
返回新的函数名我们来验证下:
<?php
create_function("", 'echo FUNCTION;');
call_user_func("\000lambda_1", 1);
?>
//输出
lambda_func因为在eval的时候, 函数名是”lambda_func”, 所以匿名函数内会输出lambda_func, 而因为最后用”\000_lambda_” . count(anonymous_functions)++重命名了函数表中的”lambda_func”函数, 所以可通过”\000_lambda_” . count(anonymous_functions)++调用这个匿名函数.
为了证实这一点, 可以将create_function的返回值dump出来查看.
而在PHP5.3发布的时候, 其中有一条new feature就是支持闭包/Lambda Function, 我第一反应是以为zval新增了一个IS_FUNCTION, 但实际上是构造了一个PHP5.3引入的Closure”类”的实例, Closure类的构造函数是私有的, 所以不能被直接实例化, 另外Closure类是Final类, 所以也不能做为基类派生子类.
//php-5.3.0
$class = new ReflectionClass("Closure");
var_dump($class->isInternal());
var_dump($class->isAbstract() );
var_dump($class->isFinal());
var_dump($class->isInterface());
//输出:
bool(true)
bool(false)
bool(true)
bool(false)
?>而PHP5.3中对闭包的支持, 也仅仅是把要保持的外部变量, 做为Closure对象的”Static属性”(并不是普通意义上的可遍历/访问的属性).
//php-5.3.0
$b = "laruence";
$func = function($a) use($b) {};
var_dump($func);
/* 输出:
object(Closure)#1 (2) {
["static"]=>
array(1) {
["b"]=>
string(8) "laruence"
}
["parameter"]=>
array(1) {
["$a"]=>
string(10) "<required>"
}
}
*/这个实现, 个人认为和JS对闭包的支持比起来, 还是有些太简陋了~
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