What are mutable variables in php?

VariableVariable is a unique variable in PHP that allows the name of a variable to be dynamically changed. Sometimes it is convenient to use variable variable names. That is, the variable name of a variable can be set and used dynamically. An ordinary variable is set through declaration, for example:

<?php
$a = &#39;hello&#39;;
?>

A variable variable obtains the value of an ordinary variable as the variable name of the variable variable. In the above example, hello can be used as a variable variable after using two dollar signs ($). For example:

<?php
$$a = &#39;world&#39;;
?>

At this time, two variables are defined: the content of $a is "hello" and the content of $hello is "world". Therefore, it can be expressed as:

<?php
echo "$a ${$a}";
?>

The following writing is more accurate and will output the same result:

<?php
echo "$a $hello";
?>

They will both output:

hello world。

The following I think it’s easier to understand! ! demo

<?
 $a="whfbbs";
 $$a=&#39;b&#39;;
 echo $whfbbs;
?>

//Output b

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