Variable variables

A variable variable looks like this: $$var

So, if $var = 'foo' and $foo = 'bar' then $$var would contain the value 'bar' because $$var can be
thought of as $'foo' which is simply $foo which has the value 'bar'.


Variable variables sound like a cryptic a useless concept, but they can be useful sometimes. For
example, if we have a configuration file consisting of configuration directives and values in this
format:

foo=bar
abc=123
Then it is very easy to read this file and create corresponding variables:


<?php
$fp = fopen('config.txt','r');
while(true) {
$line = fgets($fp,80);
if(!feof($fp)) {
if($line[0]=='#' || strlen($line)<2) continue;
list($name,$val)=explode('=',$line,2);
$$name=trim($val);
} else break;
}
fclose($fp);
?>
Along the same lines as variable variables, you can create compound variables and variable
functions.
<?php
$str = 'var';
$var_toaster = "Hello World";
echo ${$str.'_toaster'};
$str(); // Calls a function named var()
${$str.'_abc'}(); // Calls a function named var_abc()
?>

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