在PHP 7.4中重写匿名函数 [英] Rewriting an anonymous function in php 7.4

问题描述

有以下匿名递归函数:

$f = function($n) use (&$f) {
    return ($n == 1) ? 1 : $n * $f($n - 1);
};

echo $f(5); // 120

我尝试重写为7.4版，但是出现错误，请告诉我我所缺少的内容吗?

I try to rewrite to version 7.4, but there is an error, please tell me what I'm missing?

$f = fn($n) => ($n == 1) ? 1 : $n * $f($n - 1);
echo $f(5);

注意:未定义的变量:f

Notice: Undefined variable: f

致命错误:未捕获错误:函数名称必须是字符串

Fatal error: Uncaught Error: Function name must be a string

推荐答案

就像Barmar所说的那样，您不能从外部范围使用$f，因为隐式绑定发生时$f仍未定义.

Just like Barmar said, you can't use $f from the outside scope, because when the implicit binding takes place $f is still undefined.

没有什么可以阻止您以后将其作为参数传递.

There is nothing stopping you from passing it later as a parameter.

$f = fn($f, $n) => $n == 1 ? 1 : $n * $f($f, $n - 1);
echo $f($f, 5); // 120

箭头功能的工作方式是，在定义期间，它们将使用外部作用域变量的按值绑定.

The way arrow functions work, is that during definition time they will use by-value binding of the outer scope's variables.

如前所述，箭头函数使用按值变量绑定.这大致等效于对箭头函数内部使用的每个变量$x执行use($x). - https://wiki.php.net/rfc/arrow_functions_v2

将闭包分配给变量$f的操作发生在闭包的定义之后，而变量$f在其定义之前未定义.

The assignment of the closure to the variable $f happens after closure's definition and the variable $f is undefined prior to it.

据我所知，在定义箭头函数时，没有任何机制可以通过引用进行绑定.

As far as I am aware, there isn't any mechanism to bind by reference while defining arrow functions.

这篇关于在PHP 7.4中重写匿名函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！