${$item} 是什么意思？

发布于 2024-11-26 07:21:16 字数 300 浏览 1 评论 0原文

在下面的情况下，我无法理解大括号的目标，并且我没有找到有关大括号使用的严肃文档。

请参阅下面的示例：

 $var = array('a','b','c','d');

 foreach($var as $item){

       ${$item} = array();

 }

我不理解 ${$item} 的含义。

我在 foreach 循环之前和之后尝试过 var_dump 但似乎没有任何反应。

有什么想法吗？

原文

I'm not able to understand braces goal in the situation below and I find no serious documentation about braces usage.

See the example below:

 $var = array('a','b','c','d');

 foreach($var as $item){

       ${$item} = array();

 }

I'm non understanding ${$item} meaning.

I've tried with var_dump before and after foreach loop but it seems nothing happens.

Any ideas?

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混浊又暗下来 2024-12-03 07:21:16

它创建 4 个空数组：

$a, $b, $c, $d // arrays now

It creates 4 empty arrays:

$a, $b, $c, $d // arrays now

回复收藏 0 原文

夕嗳→ 2024-12-03 07:21:16

大括号创建一个与大括号内提供的字符串同名的变量。
在您的代码中，它通过从数组中获取字符串来创建 4 个新变量 $a、$b、$c、$d
$var 。

下面是一个示例，用于查看代码中创建的变量的差异：
http://codepad.org/E2619ufe

<?php

$var = array('a','b','c','d');
$currentState = get_defined_vars();

foreach($var as $item){

       ${$item} = array();

 }

$newState =  get_defined_vars();
$newVariables = array_diff(array_keys($newState),array_keys($currentState));
var_dump($newVariables);

?>

以下是大括号的用法示例：
http://codepad.org/KeE75iNP

<?php

${'myVar'} = 12345;
var_dump($myVar);

/* also helpful when the variable name contains $ due to some reason */

${'theCurrency
} = 4000;
var_dump(${'theCurrency
});

/* uncomment line below, it will raise syntax error */
//var_dump($theCurrency$); 


?>

Curly braces create a variable with same name as string provided inside the curly braces.
In your code, it creates 4 new variables $a,$b,$c,$d by taking strings from the array
$var .

Here is an example to see the difference in variables created in your code:
http://codepad.org/E2619ufe

<?php

$var = array('a','b','c','d');
$currentState = get_defined_vars();

foreach($var as $item){

       ${$item} = array();

 }

$newState =  get_defined_vars();
$newVariables = array_diff(array_keys($newState),array_keys($currentState));
var_dump($newVariables);

?>

Here is an example usage of curly braces:
http://codepad.org/KeE75iNP

<?php

${'myVar'} = 12345;
var_dump($myVar);

/* also helpful when the variable name contains $ due to some reason */

${'theCurrency
} = 4000;
var_dump(${'theCurrency
});

/* uncomment line below, it will raise syntax error */
//var_dump($theCurrency$); 


?>

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凉栀 2024-12-03 07:21:16

是的，它确实创建了 4 个空数组，您正在运行时创建变量，这就是大括号的用法。以下是大括号的用法示例： php 中的大括号

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今天小雨转甜 2024-12-03 07:21:16

花括号中放入的任何内容都将替换变量的值。

所以最终值将是 4 个空数组

${item} will become $a, ie: $a = array();
${item} will become $b, ie: $b = array();
${item} will become $c, ie: $c = array();
${item} will become $d, ie: $d = array();

Anything you put in curly brace will substitute value of the variable.

So the end value will be 4 empty arrays

${item} will become $a, ie: $a = array();
${item} will become $b, ie: $b = array();
${item} will become $c, ie: $c = array();
${item} will become $d, ie: $d = array();

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