How Does PHP's `$$` (Double Dollar) Notation Work with Variable Variables?

PHP's Variable Variables: Decoding $$ (Double Dollar)

When encountering the $$ notation within PHP, it's essential to delve into the concept of variable variables. This syntax, denoted as $$variable, allows you to access and manipulate variables whose names are stored in other variables.

Imagine the following code snippet within a function:

global $$link;

Here, $$link represents a variable variable, where $$ indicates that the variable name itself is stored in the $link variable. Consider the following example:

$real_variable = 'test';
$name = 'real_variable';
echo $$name; // Outputs: 'test'

In this case:

• $real_variable stores the value 'test'.
• $name contains the name of $real_variable ('real_variable').
• $$name translates to "the variable whose name is stored in $name," which is $real_variable.
• Therefore, $$name effectively retrieves the value of $real_variable, which is 'test'.

Note that this mechanism can extend beyond "double variables." For example:

$real_variable = 'test';
$name = 'real_variable';
$name_of_name = 'name';

echo $$name_of_name; // Outputs: 'real_variable'
echo $$$name_of_name; // Outputs: 'test'

Here, $$$name_of_name navigates one level deeper, accessing the variable whose name is stored in the variable named by $name_of_name.

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