Variables (symbolic links)

Sometimes it is convenient to have variable variable names. That is, the name of a variable that can be determined and changed dynamically. A normal variable is defined like this:

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

A variable takes the value of a variable and treats it as the name of a variable. In the above example, hello can be used as a variable name with two dollar signs. I.e:

<?php
$$a = "world";
?>

Now, the PHP symbol tree contains two variables: $ a , containing "hello", and $ hello , containing "world". Thus, the following expression:

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

will output the same as the following expression:

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

that is, they both bring out: hello world .

In order to use variable variables with arrays, you must solve the problem of ambiguity. That is, if you write $$ a [1] , the handler needs to know whether you want to use $ a [1] as a variable, or you need it as a variable $$ a , and then its index [1]. The syntax for resolving this ambiguity is as follows: $ {$ a [1]} for the first case and $ {$ a} [1] for the second.

Attention! Note that variables cannot be used with predefined PHP variables. This means that you cannot do something like $ {$ _ GET} . If you are looking for a way to use superglobal variables and old HTTP _ * _ VARS , you can try to reference them.

Variables are also called symbolic links.